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 $110.54   6.871%   $118.1352   $118.14   $118.15   $118.10  
  Purchase #2 $91.62   6.606%   $97.6724   $97.67   $97.65   $97.70  
  Purchase #3 $240.53   11.307%   $267.7267   $267.73   $267.75   $267.70  
  Purchase #4 $109.43   12.809%   $123.4469   $123.45   $123.45   $123.40  
  Purchase #5 $237.73   9.523%   $260.369   $260.37   $260.35   $260.40  
  Purchase #6 $223.81   12.775%   $252.4017   $252.40   $252.40   $252.40  
  Purchase #7 $68.42   9.631%   $75.0095   $75.01   $75.00   $75.00  
  7 purchase totals = $1,082.08       $1,194.7614   $1,194.77   $1,194.75   $1,194.70