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 $241.89   6.116%   $256.684   $256.68   $256.70   $256.70  
  Purchase #2 $202.34   5.449%   $213.3655   $213.37   $213.35   $213.40  
  Purchase #3 $178.54   12.294%   $200.4897   $200.49   $200.50   $200.50  
  Purchase #4 $58.29   6.304%   $61.9646   $61.96   $61.95   $62.00  
  Purchase #5 $29.76   8.296%   $32.2289   $32.23   $32.25   $32.20  
  Purchase #6 $204.77   4.772%   $214.5416   $214.54   $214.55   $214.50  
  Purchase #7 $249.89   13.114%   $282.6606   $282.66   $282.65   $282.70  
  7 purchase totals = $1,165.48       $1,261.9349   $1,261.93   $1,261.95   $1,262.00