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 $207.33   13.345%   $234.9982   $235.00   $235.00   $235.00  
  Purchase #2 $151.38   5.553%   $159.7861   $159.79   $159.80   $159.80  
  Purchase #3 $54.84   13.161%   $62.0575   $62.06   $62.05   $62.10  
  Purchase #4 $93.79   7.395%   $100.7258   $100.73   $100.75   $100.70  
  Purchase #5 $141.49   11.740%   $158.1009   $158.10   $158.10   $158.10  
  Purchase #6 $16.78   3.696%   $17.4002   $17.40   $17.40   $17.40  
  Purchase #7 $61.85   6.478%   $65.8566   $65.86   $65.85   $65.90  
  7 purchase totals = $727.46       $798.9253   $798.94   $798.95   $799.00