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 $112.71   8.764%   $122.5879   $122.59   $122.60   $122.60  
  Purchase #2 $244.33   12.660%   $275.2622   $275.26   $275.25   $275.30  
  Purchase #3 $177.89   10.534%   $196.6289   $196.63   $196.65   $196.60  
  Purchase #4 $97.47   12.522%   $109.6752   $109.68   $109.70   $109.70  
  Purchase #5 $79.77   9.867%   $87.6409   $87.64   $87.65   $87.60  
  Purchase #6 $32.59   11.611%   $36.374   $36.37   $36.35   $36.40  
  Purchase #7 $96.88   7.594%   $104.2371   $104.24   $104.25   $104.20  
  7 purchase totals = $841.64       $932.4062   $932.41   $932.45   $932.40