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 $14.81   10.674%   $16.3908   $16.39   $16.40   $16.40  
  Purchase #2 $58.30   7.623%   $62.7442   $62.74   $62.75   $62.70  
  Purchase #3 $35.27   7.692%   $37.983   $37.98   $38.00   $38.00  
  Purchase #4 $22.62   5.673%   $23.9032   $23.90   $23.90   $23.90  
  Purchase #5 $116.65   7.648%   $125.5714   $125.57   $125.55   $125.60  
  Purchase #6 $232.32   12.130%   $260.5004   $260.50   $260.50   $260.50  
  Purchase #7 $54.98   5.339%   $57.9154   $57.92   $57.90   $57.90  
  7 purchase totals = $534.95       $585.0084   $585.00   $585.00   $585.00