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 $62.91   6.698%   $67.1237   $67.12   $67.10   $67.10  
  Purchase #2 $164.68   10.727%   $182.3452   $182.35   $182.35   $182.30  
  Purchase #3 $131.45   3.372%   $135.8825   $135.88   $135.90   $135.90  
  Purchase #4 $226.31   12.277%   $254.0941   $254.09   $254.10   $254.10  
  Purchase #5 $34.63   13.146%   $39.1825   $39.18   $39.20   $39.20  
  Purchase #6 $89.59   6.855%   $95.7314   $95.73   $95.75   $95.70  
  Purchase #7 $9.61   10.519%   $10.6209   $10.62   $10.60   $10.60  
  7 purchase totals = $719.18       $784.9803   $784.97   $785.00   $784.90