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 $87.75   12.168%   $98.4274   $98.43   $98.45   $98.40  
  Purchase #2 $85.69   6.246%   $91.0422   $91.04   $91.05   $91.00  
  Purchase #3 $158.41   5.786%   $167.5756   $167.58   $167.60   $167.60  
  Purchase #4 $13.86   12.111%   $15.5386   $15.54   $15.55   $15.50  
  Purchase #5 $121.92   3.538%   $126.2335   $126.23   $126.25   $126.20  
  Purchase #6 $117.62   8.792%   $127.9612   $127.96   $127.95   $128.00  
  Purchase #7 $120.87   12.339%   $135.7841   $135.78   $135.80   $135.80  
  7 purchase totals = $706.12       $762.5626   $762.56   $762.65   $762.50