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 $68.28   13.711%   $77.6419   $77.64   $77.65   $77.60  
  Purchase #2 $13.72   11.457%   $15.2919   $15.29   $15.30   $15.30  
  Purchase #3 $171.28   4.559%   $179.0887   $179.09   $179.10   $179.10  
  Purchase #4 $84.41   5.356%   $88.931   $88.93   $88.95   $88.90  
  Purchase #5 $205.36   4.874%   $215.3692   $215.37   $215.35   $215.40  
  Purchase #6 $149.81   10.265%   $165.188   $165.19   $165.20   $165.20  
  Purchase #7 $179.53   7.378%   $192.7757   $192.78   $192.80   $192.80  
  7 purchase totals = $872.39       $934.2864   $934.29   $934.35   $934.30