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 $46.92   12.136%   $52.6142   $52.61   $52.60   $52.60  
  Purchase #2 $12.56   3.640%   $13.0172   $13.02   $13.00   $13.00  
  Purchase #3 $221.89   5.402%   $233.8765   $233.88   $233.90   $233.90  
  Purchase #4 $60.64   3.370%   $62.6836   $62.68   $62.70   $62.70  
  Purchase #5 $57.62   13.372%   $65.3249   $65.32   $65.30   $65.30  
  Purchase #6 $170.88   13.683%   $194.2615   $194.26   $194.25   $194.30  
  Purchase #7 $144.48   10.677%   $159.9061   $159.91   $159.90   $159.90  
  7 purchase totals = $714.99       $781.6840   $781.68   $781.65   $781.70