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 $117.89   7.533%   $126.7707   $126.77   $126.75   $126.80  
  Purchase #2 $150.95   9.844%   $165.8095   $165.81   $165.80   $165.80  
  Purchase #3 $178.62   13.226%   $202.2443   $202.24   $202.25   $202.20  
  Purchase #4 $52.69   8.141%   $56.9795   $56.98   $57.00   $57.00  
  Purchase #5 $12.50   5.808%   $13.226   $13.23   $13.25   $13.20  
  Purchase #6 $54.50   6.366%   $57.9695   $57.97   $57.95   $58.00  
  Purchase #7 $221.56   4.870%   $232.35   $232.35   $232.35   $232.40  
  7 purchase totals = $788.71       $855.3495   $855.35   $855.35   $855.40