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 $88.74   6.243%   $94.28   $94.28   $94.30   $94.30  
  Purchase #2 $224.47   5.497%   $236.8091   $236.81   $236.80   $236.80  
  Purchase #3 $5.78   10.656%   $6.3959   $6.40   $6.40   $6.40  
  Purchase #4 $115.47   7.747%   $124.4155   $124.42   $124.40   $124.40  
  Purchase #5 $58.75   8.624%   $63.8166   $63.82   $63.80   $63.80  
  Purchase #6 $230.66   6.837%   $246.4302   $246.43   $246.45   $246.40  
  Purchase #7 $48.66   8.826%   $52.9547   $52.95   $52.95   $53.00  
  7 purchase totals = $772.53       $825.1020   $825.11   $825.10   $825.10