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 $68.73   11.205%   $76.4312   $76.43   $76.45   $76.40  
  Purchase #2 $163.72   13.806%   $186.3232   $186.32   $186.30   $186.30  
  Purchase #3 $172.88   9.305%   $188.9665   $188.97   $188.95   $189.00  
  Purchase #4 $144.72   6.352%   $153.9126   $153.91   $153.90   $153.90  
  Purchase #5 $95.57   9.831%   $104.9655   $104.97   $104.95   $105.00  
  Purchase #6 $162.77   12.164%   $182.5693   $182.57   $182.55   $182.60  
  Purchase #7 $94.39   7.490%   $101.4598   $101.46   $101.45   $101.50  
  7 purchase totals = $902.78       $994.6281   $994.63   $994.55   $994.70