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 $53.69   7.502%   $57.7178   $57.72   $57.70   $57.70  
  Purchase #2 $233.82   5.832%   $247.4564   $247.46   $247.45   $247.50  
  Purchase #3 $118.61   13.862%   $135.0517   $135.05   $135.05   $135.10  
  Purchase #4 $164.29   11.750%   $183.5941   $183.59   $183.60   $183.60  
  Purchase #5 $165.47   8.413%   $179.391   $179.39   $179.40   $179.40  
  Purchase #6 $202.72   3.834%   $210.4923   $210.49   $210.50   $210.50  
  Purchase #7 $13.67   4.779%   $14.3233   $14.32   $14.30   $14.30  
  7 purchase totals = $952.27       $1,028.0266   $1,028.02   $1,028.00   $1,028.10