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 $45.97   13.568%   $52.2072   $52.21   $52.20   $52.20  
  Purchase #2 $191.26   7.522%   $205.6466   $205.65   $205.65   $205.60  
  Purchase #3 $111.44   13.366%   $126.3351   $126.34   $126.35   $126.30  
  Purchase #4 $158.50   11.717%   $177.0714   $177.07   $177.05   $177.10  
  Purchase #5 $182.79   4.810%   $191.5822   $191.58   $191.60   $191.60  
  Purchase #6 $75.35   12.500%   $84.7688   $84.77   $84.75   $84.80  
  Purchase #7 $17.50   6.230%   $18.5903   $18.59   $18.60   $18.60  
  7 purchase totals = $782.81       $856.2016   $856.21   $856.20   $856.20