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 $86.29   7.568%   $92.8204   $92.82   $92.80   $92.80  
  Purchase #2 $63.55   11.654%   $70.9561   $70.96   $70.95   $71.00  
  Purchase #3 $242.62   11.277%   $269.9803   $269.98   $270.00   $270.00  
  Purchase #4 $200.90   6.175%   $213.3056   $213.31   $213.30   $213.30  
  Purchase #5 $109.67   7.596%   $118.0005   $118.00   $118.00   $118.00  
  Purchase #6 $16.77   11.819%   $18.752   $18.75   $18.75   $18.80  
  Purchase #7 $9.83   6.642%   $10.4829   $10.48   $10.50   $10.50  
  7 purchase totals = $729.63       $794.2978   $794.30   $794.30   $794.40