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 $60.97   7.613%   $65.6116   $65.61   $65.60   $65.60  
  Purchase #2 $134.67   8.822%   $146.5506   $146.55   $146.55   $146.60  
  Purchase #3 $249.86   9.175%   $272.7847   $272.78   $272.80   $272.80  
  Purchase #4 $98.32   9.513%   $107.6732   $107.67   $107.65   $107.70  
  Purchase #5 $102.76   5.703%   $108.6204   $108.62   $108.60   $108.60  
  Purchase #6 $101.98   6.403%   $108.5098   $108.51   $108.50   $108.50  
  Purchase #7 $193.56   12.247%   $217.2653   $217.27   $217.25   $217.30  
  7 purchase totals = $942.12       $1,027.0156   $1,027.01   $1,026.95   $1,027.10