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 $57.72   10.135%   $63.5699   $63.57   $63.55   $63.60  
  Purchase #2 $60.48   7.306%   $64.8987   $64.90   $64.90   $64.90  
  Purchase #3 $96.82   6.259%   $102.88   $102.88   $102.90   $102.90  
  Purchase #4 $48.37   3.447%   $50.0373   $50.04   $50.05   $50.00  
  Purchase #5 $199.89   6.549%   $212.9808   $212.98   $213.00   $213.00  
  Purchase #6 $125.92   8.671%   $136.8385   $136.84   $136.85   $136.80  
  Purchase #7 $198.72   4.841%   $208.34   $208.34   $208.35   $208.30  
  7 purchase totals = $787.92       $839.5452   $839.55   $839.60   $839.50