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 $76.66   9.435%   $83.8929   $83.89   $83.90   $83.90  
  Purchase #2 $216.41   11.562%   $241.4313   $241.43   $241.45   $241.40  
  Purchase #3 $189.83   9.181%   $207.2583   $207.26   $207.25   $207.30  
  Purchase #4 $131.51   13.726%   $149.5611   $149.56   $149.55   $149.60  
  Purchase #5 $51.58   4.186%   $53.7391   $53.74   $53.75   $53.70  
  Purchase #6 $200.29   10.515%   $221.3505   $221.35   $221.35   $221.40  
  Purchase #7 $68.97   9.398%   $75.4518   $75.45   $75.45   $75.50  
  7 purchase totals = $935.25       $1,032.6850   $1,032.68   $1,032.70   $1,032.80