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 $164.59   11.448%   $183.4323   $183.43   $183.45   $183.40  
  Purchase #2 $63.99   9.428%   $70.023   $70.02   $70.00   $70.00  
  Purchase #3 $247.61   3.601%   $256.5264   $256.53   $256.55   $256.50  
  Purchase #4 $5.56   6.647%   $5.9296   $5.93   $5.95   $5.90  
  Purchase #5 $129.42   13.754%   $147.2204   $147.22   $147.20   $147.20  
  Purchase #6 $234.82   11.137%   $260.9719   $260.97   $260.95   $261.00  
  Purchase #7 $173.38   3.316%   $179.1293   $179.13   $179.15   $179.10  
  7 purchase totals = $1,019.37       $1,103.2329   $1,103.23   $1,103.25   $1,103.10