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 $88.28   5.855%   $93.4488   $93.45   $93.45   $93.40  
  Purchase #2 $130.65   4.814%   $136.9395   $136.94   $136.95   $136.90  
  Purchase #3 $221.77   11.422%   $247.1006   $247.10   $247.10   $247.10  
  Purchase #4 $49.88   9.389%   $54.5632   $54.56   $54.55   $54.60  
  Purchase #5 $244.32   8.512%   $265.1165   $265.12   $265.10   $265.10  
  Purchase #6 $26.44   8.569%   $28.7056   $28.71   $28.70   $28.70  
  Purchase #7 $124.41   8.278%   $134.7087   $134.71   $134.70   $134.70  
  7 purchase totals = $885.75       $960.5829   $960.59   $960.55   $960.50