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 $61.49   4.453%   $64.2281   $64.23   $64.25   $64.20  
  Purchase #2 $120.51   11.475%   $134.3385   $134.34   $134.35   $134.30  
  Purchase #3 $194.75   12.355%   $218.8114   $218.81   $218.80   $218.80  
  Purchase #4 $158.91   5.611%   $167.8264   $167.83   $167.85   $167.80  
  Purchase #5 $6.39   12.323%   $7.1774   $7.18   $7.20   $7.20  
  Purchase #6 $161.70   10.106%   $178.0414   $178.04   $178.05   $178.00  
  Purchase #7 $240.48   4.272%   $250.7533   $250.75   $250.75   $250.80  
  7 purchase totals = $944.23       $1,021.1765   $1,021.18   $1,021.25   $1,021.10