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 $98.34   13.644%   $111.7575   $111.76   $111.75   $111.80  
  Purchase #2 $40.36   10.109%   $44.44   $44.44   $44.45   $44.40  
  Purchase #3 $63.93   9.741%   $70.1574   $70.16   $70.15   $70.20  
  Purchase #4 $235.56   9.211%   $257.2574   $257.26   $257.25   $257.30  
  Purchase #5 $199.87   9.848%   $219.5532   $219.55   $219.55   $219.60  
  Purchase #6 $227.75   3.688%   $236.1494   $236.15   $236.15   $236.10  
  Purchase #7 $9.91   11.280%   $11.0278   $11.03   $11.05   $11.00  
  7 purchase totals = $875.72       $950.3427   $950.35   $950.35   $950.40