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 $190.93   9.260%   $208.6101   $208.61   $208.60   $208.60  
  Purchase #2 $74.56   8.658%   $81.0154   $81.02   $81.00   $81.00  
  Purchase #3 $144.78   6.571%   $154.2935   $154.29   $154.30   $154.30  
  Purchase #4 $95.94   5.272%   $100.998   $101.00   $101.00   $101.00  
  Purchase #5 $206.42   11.414%   $229.9808   $229.98   $230.00   $230.00  
  Purchase #6 $105.54   10.351%   $116.4644   $116.46   $116.45   $116.50  
  Purchase #7 $108.76   9.812%   $119.4315   $119.43   $119.45   $119.40  
  7 purchase totals = $926.93       $1,010.7937   $1,010.79   $1,010.80   $1,010.80