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 $83.73   13.136%   $94.7288   $94.73   $94.75   $94.70  
  Purchase #2 $236.64   4.331%   $246.8889   $246.89   $246.90   $246.90  
  Purchase #3 $212.36   8.171%   $229.7119   $229.71   $229.70   $229.70  
  Purchase #4 $35.73   3.451%   $36.963   $36.96   $36.95   $37.00  
  Purchase #5 $68.38   4.647%   $71.5576   $71.56   $71.55   $71.60  
  Purchase #6 $60.53   4.716%   $63.3846   $63.38   $63.40   $63.40  
  Purchase #7 $238.88   5.305%   $251.5526   $251.55   $251.55   $251.60  
  7 purchase totals = $936.25       $994.7874   $994.78   $994.80   $994.90