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 $41.58   7.394%   $44.6544   $44.65   $44.65   $44.70  
  Purchase #2 $102.47   9.843%   $112.5561   $112.56   $112.55   $112.60  
  Purchase #3 $25.80   5.168%   $27.1333   $27.13   $27.15   $27.10  
  Purchase #4 $107.88   12.630%   $121.5052   $121.51   $121.50   $121.50  
  Purchase #5 $27.71   5.670%   $29.2812   $29.28   $29.30   $29.30  
  Purchase #6 $93.96   12.493%   $105.6984   $105.70   $105.70   $105.70  
  Purchase #7 $150.64   13.643%   $171.1918   $171.19   $171.20   $171.20  
  7 purchase totals = $550.04       $612.0204   $612.02   $612.05   $612.10