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 $219.30   7.437%   $235.6093   $235.61   $235.60   $235.60  
  Purchase #2 $135.90   5.137%   $142.8812   $142.88   $142.90   $142.90  
  Purchase #3 $87.37   13.109%   $98.8233   $98.82   $98.80   $98.80  
  Purchase #4 $52.70   11.466%   $58.7426   $58.74   $58.75   $58.70  
  Purchase #5 $103.67   13.346%   $117.5058   $117.51   $117.50   $117.50  
  Purchase #6 $170.63   13.439%   $193.561   $193.56   $193.55   $193.60  
  Purchase #7 $236.45   7.862%   $255.0397   $255.04   $255.05   $255.00  
  7 purchase totals = $1,006.02       $1,102.1629   $1,102.16   $1,102.15   $1,102.10