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 $56.31   9.492%   $61.6549   $61.65   $61.65   $61.70  
  Purchase #2 $171.46   13.381%   $194.4031   $194.40   $194.40   $194.40  
  Purchase #3 $184.57   12.593%   $207.8129   $207.81   $207.80   $207.80  
  Purchase #4 $23.92   13.149%   $27.0652   $27.07   $27.05   $27.10  
  Purchase #5 $83.96   5.811%   $88.8389   $88.84   $88.85   $88.80  
  Purchase #6 $164.37   13.431%   $186.4465   $186.45   $186.45   $186.40  
  Purchase #7 $195.86   3.351%   $202.4233   $202.42   $202.40   $202.40  
  7 purchase totals = $880.45       $968.6448   $968.64   $968.60   $968.60