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 $59.56   5.104%   $62.5999   $62.60   $62.60   $62.60  
  Purchase #2 $52.97   8.754%   $57.607   $57.61   $57.60   $57.60  
  Purchase #3 $99.36   4.640%   $103.9703   $103.97   $103.95   $104.00  
  Purchase #4 $93.45   5.132%   $98.2459   $98.25   $98.25   $98.20  
  Purchase #5 $21.41   12.703%   $24.1297   $24.13   $24.15   $24.10  
  Purchase #6 $104.72   6.340%   $111.3592   $111.36   $111.35   $111.40  
  Purchase #7 $188.52   11.545%   $210.2846   $210.28   $210.30   $210.30  
  7 purchase totals = $619.99       $668.1966   $668.20   $668.20   $668.20