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 $62.78   7.208%   $67.3052   $67.31   $67.30   $67.30  
  Purchase #2 $183.43   13.304%   $207.8335   $207.83   $207.85   $207.80  
  Purchase #3 $33.54   12.297%   $37.6644   $37.66   $37.65   $37.70  
  Purchase #4 $216.71   9.385%   $237.0482   $237.05   $237.05   $237.00  
  Purchase #5 $97.26   10.626%   $107.5948   $107.59   $107.60   $107.60  
  Purchase #6 $108.94   10.279%   $120.1379   $120.14   $120.15   $120.10  
  Purchase #7 $202.51   3.789%   $210.1831   $210.18   $210.20   $210.20  
  7 purchase totals = $905.17       $987.7671   $987.76   $987.80   $987.70