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 $206.26   13.750%   $234.6208   $234.62   $234.60   $234.60  
  Purchase #2 $31.60   9.616%   $34.6387   $34.64   $34.65   $34.60  
  Purchase #3 $209.81   5.228%   $220.7789   $220.78   $220.80   $220.80  
  Purchase #4 $167.38   3.485%   $173.2132   $173.21   $173.20   $173.20  
  Purchase #5 $20.28   13.491%   $23.016   $23.02   $23.00   $23.00  
  Purchase #6 $101.75   3.773%   $105.589   $105.59   $105.60   $105.60  
  Purchase #7 $186.29   8.595%   $202.3016   $202.30   $202.30   $202.30  
  7 purchase totals = $923.37       $994.1582   $994.16   $994.15   $994.10