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 $116.83   11.183%   $129.8951   $129.90   $129.90   $129.90  
  Purchase #2 $235.92   4.779%   $247.1946   $247.19   $247.20   $247.20  
  Purchase #3 $183.72   11.259%   $204.405   $204.41   $204.40   $204.40  
  Purchase #4 $39.31   10.171%   $43.3082   $43.31   $43.30   $43.30  
  Purchase #5 $184.70   11.169%   $205.3291   $205.33   $205.35   $205.30  
  Purchase #6 $48.59   13.416%   $55.1088   $55.11   $55.10   $55.10  
  Purchase #7 $127.52   10.792%   $141.282   $141.28   $141.30   $141.30  
  7 purchase totals = $936.59       $1,026.5228   $1,026.53   $1,026.55   $1,026.50