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 $224.37   13.623%   $254.9359   $254.94   $254.95   $254.90  
  Purchase #2 $125.71   4.131%   $130.9031   $130.90   $130.90   $130.90  
  Purchase #3 $61.47   4.728%   $64.3763   $64.38   $64.40   $64.40  
  Purchase #4 $238.41   6.259%   $253.3321   $253.33   $253.35   $253.30  
  Purchase #5 $237.36   6.842%   $253.6002   $253.60   $253.60   $253.60  
  Purchase #6 $216.44   13.360%   $245.3564   $245.36   $245.35   $245.40  
  Purchase #7 $173.94   9.797%   $190.9809   $190.98   $191.00   $191.00  
  7 purchase totals = $1,277.70       $1,393.4849   $1,393.49   $1,393.55   $1,393.50