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 $94.37   12.546%   $106.2097   $106.21   $106.20   $106.20  
  Purchase #2 $82.36   7.121%   $88.2249   $88.22   $88.20   $88.20  
  Purchase #3 $22.85   7.530%   $24.5706   $24.57   $24.55   $24.60  
  Purchase #4 $126.26   11.797%   $141.1549   $141.15   $141.15   $141.20  
  Purchase #5 $43.33   11.685%   $48.3931   $48.39   $48.40   $48.40  
  Purchase #6 $238.52   8.384%   $258.5175   $258.52   $258.50   $258.50  
  Purchase #7 $115.35   10.332%   $127.268   $127.27   $127.25   $127.30  
  7 purchase totals = $723.04       $794.3387   $794.33   $794.25   $794.40