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 $53.60   13.351%   $60.7561   $60.76   $60.75   $60.80  
  Purchase #2 $200.84   6.199%   $213.2901   $213.29   $213.30   $213.30  
  Purchase #3 $116.83   7.477%   $125.5654   $125.57   $125.55   $125.60  
  Purchase #4 $228.83   13.667%   $260.1042   $260.10   $260.10   $260.10  
  Purchase #5 $222.69   5.506%   $234.9513   $234.95   $234.95   $235.00  
  Purchase #6 $122.46   6.640%   $130.5913   $130.59   $130.60   $130.60  
  Purchase #7 $164.35   11.131%   $182.6438   $182.64   $182.65   $182.60  
  7 purchase totals = $1,109.60       $1,207.9022   $1,207.90   $1,207.90   $1,208.00