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 $49.95   9.320%   $54.6053   $54.61   $54.60   $54.60  
  Purchase #2 $53.98   5.230%   $56.8032   $56.80   $56.80   $56.80  
  Purchase #3 $218.94   11.787%   $244.7465   $244.75   $244.75   $244.70  
  Purchase #4 $21.59   6.170%   $22.9221   $22.92   $22.90   $22.90  
  Purchase #5 $108.64   8.453%   $117.8233   $117.82   $117.80   $117.80  
  Purchase #6 $95.90   8.544%   $104.0937   $104.09   $104.10   $104.10  
  Purchase #7 $158.91   3.702%   $164.7928   $164.79   $164.80   $164.80  
  7 purchase totals = $707.91       $765.7869   $765.78   $765.75   $765.70