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 $119.75   5.791%   $126.6847   $126.68   $126.70   $126.70  
  Purchase #2 $96.72   9.309%   $105.7237   $105.72   $105.70   $105.70  
  Purchase #3 $178.46   13.501%   $202.5539   $202.55   $202.55   $202.60  
  Purchase #4 $85.61   5.454%   $90.2792   $90.28   $90.30   $90.30  
  Purchase #5 $108.30   12.679%   $122.0314   $122.03   $122.05   $122.00  
  Purchase #6 $217.54   11.255%   $242.0241   $242.02   $242.00   $242.00  
  Purchase #7 $29.95   11.611%   $33.4275   $33.43   $33.45   $33.40  
  7 purchase totals = $836.33       $922.7245   $922.71   $922.75   $922.70