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 $124.93   3.499%   $129.3013   $129.30   $129.30   $129.30  
  Purchase #2 $235.40   10.316%   $259.6839   $259.68   $259.70   $259.70  
  Purchase #3 $231.45   13.280%   $262.1866   $262.19   $262.20   $262.20  
  Purchase #4 $127.55   6.144%   $135.3867   $135.39   $135.40   $135.40  
  Purchase #5 $187.62   13.607%   $213.1495   $213.15   $213.15   $213.10  
  Purchase #6 $234.58   4.315%   $244.7021   $244.70   $244.70   $244.70  
  Purchase #7 $82.98   11.740%   $92.7219   $92.72   $92.70   $92.70  
  7 purchase totals = $1,224.51       $1,337.1320   $1,337.13   $1,337.15   $1,337.10