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 $56.87   11.852%   $63.6102   $63.61   $63.60   $63.60  
  Purchase #2 $61.26   4.373%   $63.9389   $63.94   $63.95   $63.90  
  Purchase #3 $49.64   5.478%   $52.3593   $52.36   $52.35   $52.40  
  Purchase #4 $92.62   7.559%   $99.6211   $99.62   $99.60   $99.60  
  Purchase #5 $91.38   13.411%   $103.635   $103.64   $103.65   $103.60  
  Purchase #6 $87.50   10.820%   $96.9675   $96.97   $96.95   $97.00  
  Purchase #7 $204.92   10.349%   $226.1272   $226.13   $226.15   $226.10  
  7 purchase totals = $644.19       $706.2592   $706.27   $706.25   $706.20