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 $67.35   9.114%   $73.4883   $73.49   $73.50   $73.50  
  Purchase #2 $177.26   5.407%   $186.8444   $186.84   $186.85   $186.80  
  Purchase #3 $211.42   9.278%   $231.0355   $231.04   $231.05   $231.00  
  Purchase #4 $108.59   10.482%   $119.9724   $119.97   $119.95   $120.00  
  Purchase #5 $189.78   12.390%   $213.2937   $213.29   $213.30   $213.30  
  Purchase #6 $116.74   5.303%   $122.9307   $122.93   $122.95   $122.90  
  Purchase #7 $60.89   11.596%   $67.9508   $67.95   $67.95   $68.00  
  7 purchase totals = $932.03       $1,015.5158   $1,015.51   $1,015.55   $1,015.50