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 $105.58   11.744%   $117.9793   $117.98   $118.00   $118.00  
  Purchase #2 $126.57   3.664%   $131.2075   $131.21   $131.20   $131.20  
  Purchase #3 $151.98   12.743%   $171.3468   $171.35   $171.35   $171.30  
  Purchase #4 $133.96   11.837%   $149.8168   $149.82   $149.80   $149.80  
  Purchase #5 $177.61   9.784%   $194.9874   $194.99   $195.00   $195.00  
  Purchase #6 $109.75   6.716%   $117.1208   $117.12   $117.10   $117.10  
  Purchase #7 $62.77   10.783%   $69.5385   $69.54   $69.55   $69.50  
  7 purchase totals = $868.22       $951.9971   $952.01   $952.00   $951.90