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 $87.83   5.590%   $92.7397   $92.74   $92.75   $92.70  
  Purchase #2 $54.78   4.756%   $57.3853   $57.39   $57.40   $57.40  
  Purchase #3 $25.29   10.774%   $28.0147   $28.01   $28.00   $28.00  
  Purchase #4 $94.33   9.473%   $103.2659   $103.27   $103.25   $103.30  
  Purchase #5 $245.34   13.648%   $278.824   $278.82   $278.80   $278.80  
  Purchase #6 $178.65   12.512%   $201.0027   $201.00   $201.00   $201.00  
  Purchase #7 $178.74   3.686%   $185.3284   $185.33   $185.35   $185.30  
  7 purchase totals = $864.96       $946.5607   $946.56   $946.55   $946.50