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 $51.86   5.321%   $54.6195   $54.62   $54.60   $54.60  
  Purchase #2 $87.82   11.445%   $97.871   $97.87   $97.85   $97.90  
  Purchase #3 $68.47   5.782%   $72.4289   $72.43   $72.45   $72.40  
  Purchase #4 $177.83   12.637%   $200.3024   $200.30   $200.30   $200.30  
  Purchase #5 $160.35   4.126%   $166.966   $166.97   $166.95   $167.00  
  Purchase #6 $93.80   5.149%   $98.6298   $98.63   $98.65   $98.60  
  Purchase #7 $235.28   13.662%   $267.424   $267.42   $267.40   $267.40  
  7 purchase totals = $875.41       $958.2416   $958.24   $958.20   $958.20