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 $168.67   13.813%   $191.9684   $191.97   $191.95   $192.00  
  Purchase #2 $21.37   9.740%   $23.4514   $23.45   $23.45   $23.50  
  Purchase #3 $101.45   13.426%   $115.0707   $115.07   $115.05   $115.10  
  Purchase #4 $167.95   7.358%   $180.3078   $180.31   $180.30   $180.30  
  Purchase #5 $49.60   10.310%   $54.7138   $54.71   $54.70   $54.70  
  Purchase #6 $117.35   6.636%   $125.1373   $125.14   $125.15   $125.10  
  Purchase #7 $13.74   9.206%   $15.0049   $15.00   $15.00   $15.00  
  7 purchase totals = $640.13       $705.6543   $705.65   $705.60   $705.70