Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.48   11.698%   $229.5171   $229.52   $229.50   $229.50  
  Purchase #2 $228.90   6.330%   $243.3894   $243.39   $243.40   $243.40  
  Purchase #3 $227.67   10.276%   $251.0654   $251.07   $251.05   $251.10  
  Purchase #4 $102.95   3.217%   $106.2619   $106.26   $106.25   $106.30  
  Purchase #5 $191.65   10.275%   $211.342   $211.34   $211.35   $211.30  
  Purchase #6 $111.53   4.102%   $116.105   $116.11   $116.10   $116.10  
  Purchase #7 $93.37   10.481%   $103.1561   $103.16   $103.15   $103.20  
  7 purchase totals = $1,161.55       $1,260.8369   $1,260.85   $1,260.80   $1,260.90