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 $59.49   9.221%   $64.9756   $64.98   $65.00   $65.00  
  Purchase #2 $213.82   9.354%   $233.8207   $233.82   $233.80   $233.80  
  Purchase #3 $244.79   3.867%   $254.256   $254.26   $254.25   $254.30  
  Purchase #4 $25.55   5.257%   $26.8932   $26.89   $26.90   $26.90  
  Purchase #5 $119.53   7.215%   $128.1541   $128.15   $128.15   $128.20  
  Purchase #6 $87.85   6.156%   $93.258   $93.26   $93.25   $93.30  
  Purchase #7 $35.96   9.738%   $39.4618   $39.46   $39.45   $39.50  
  7 purchase totals = $786.99       $840.8194   $840.82   $840.80   $841.00