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 $49.45   12.751%   $55.7554   $55.76   $55.75   $55.80  
  Purchase #2 $116.26   8.392%   $126.0165   $126.02   $126.00   $126.00  
  Purchase #3 $88.68   5.617%   $93.6612   $93.66   $93.65   $93.70  
  Purchase #4 $202.49   11.821%   $226.4263   $226.43   $226.45   $226.40  
  Purchase #5 $146.80   7.269%   $157.4709   $157.47   $157.45   $157.50  
  Purchase #6 $189.65   13.821%   $215.8615   $215.86   $215.85   $215.90  
  Purchase #7 $54.58   8.289%   $59.1041   $59.10   $59.10   $59.10  
  7 purchase totals = $847.91       $934.2959   $934.30   $934.25   $934.40