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 $184.34   12.448%   $207.2866   $207.29   $207.30   $207.30  
  Purchase #2 $54.66   13.494%   $62.0358   $62.04   $62.05   $62.00  
  Purchase #3 $45.80   3.666%   $47.479   $47.48   $47.50   $47.50  
  Purchase #4 $159.36   12.370%   $179.0728   $179.07   $179.05   $179.10  
  Purchase #5 $58.60   7.233%   $62.8385   $62.84   $62.85   $62.80  
  Purchase #6 $120.76   4.470%   $126.158   $126.16   $126.15   $126.20  
  Purchase #7 $23.27   10.127%   $25.6266   $25.63   $25.65   $25.60  
  7 purchase totals = $646.79       $710.4973   $710.51   $710.55   $710.50