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 $56.27   6.140%   $59.725   $59.73   $59.75   $59.70  
  Purchase #2 $237.98   6.746%   $254.0341   $254.03   $254.05   $254.00  
  Purchase #3 $13.95   10.698%   $15.4424   $15.44   $15.45   $15.40  
  Purchase #4 $248.29   8.366%   $269.0619   $269.06   $269.05   $269.10  
  Purchase #5 $180.91   4.413%   $188.8936   $188.89   $188.90   $188.90  
  Purchase #6 $241.67   10.616%   $267.3257   $267.33   $267.35   $267.30  
  Purchase #7 $231.60   10.719%   $256.4252   $256.43   $256.45   $256.40  
  7 purchase totals = $1,210.67       $1,310.9079   $1,310.91   $1,311.00   $1,310.80