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 $85.62   11.298%   $95.2933   $95.29   $95.30   $95.30  
  Purchase #2 $43.90   12.672%   $49.463   $49.46   $49.45   $49.50  
  Purchase #3 $201.61   5.520%   $212.7389   $212.74   $212.75   $212.70  
  Purchase #4 $76.46   12.175%   $85.769   $85.77   $85.75   $85.80  
  Purchase #5 $148.82   6.176%   $158.0111   $158.01   $158.00   $158.00  
  Purchase #6 $9.40   9.279%   $10.2722   $10.27   $10.25   $10.30  
  Purchase #7 $203.64   12.235%   $228.5554   $228.56   $228.55   $228.60  
  7 purchase totals = $769.45       $840.1029   $840.10   $840.05   $840.20