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 $159.43   10.827%   $176.6915   $176.69   $176.70   $176.70  
  Purchase #2 $143.30   10.347%   $158.1273   $158.13   $158.15   $158.10  
  Purchase #3 $65.64   3.609%   $68.0089   $68.01   $68.00   $68.00  
  Purchase #4 $5.90   5.845%   $6.2449   $6.24   $6.25   $6.20  
  Purchase #5 $188.63   4.781%   $197.6484   $197.65   $197.65   $197.60  
  Purchase #6 $209.84   10.564%   $232.0075   $232.01   $232.00   $232.00  
  Purchase #7 $51.39   10.433%   $56.7515   $56.75   $56.75   $56.80  
  7 purchase totals = $824.13       $895.4800   $895.48   $895.50   $895.40