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 $83.99   11.432%   $93.5917   $93.59   $93.60   $93.60  
  Purchase #2 $217.89   10.288%   $240.3065   $240.31   $240.30   $240.30  
  Purchase #3 $106.66   5.452%   $112.4751   $112.48   $112.50   $112.50  
  Purchase #4 $150.26   7.453%   $161.4589   $161.46   $161.45   $161.50  
  Purchase #5 $189.53   6.428%   $201.713   $201.71   $201.70   $201.70  
  Purchase #6 $136.96   10.242%   $150.9874   $150.99   $151.00   $151.00  
  Purchase #7 $249.95   9.525%   $273.7577   $273.76   $273.75   $273.80  
  7 purchase totals = $1,135.24       $1,234.2903   $1,234.30   $1,234.30   $1,234.40