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 $240.47   10.621%   $266.0103   $266.01   $266.00   $266.00  
  Purchase #2 $99.71   11.157%   $110.8346   $110.83   $110.85   $110.80  
  Purchase #3 $167.25   5.635%   $176.6745   $176.67   $176.65   $176.70  
  Purchase #4 $157.59   7.282%   $169.0657   $169.07   $169.05   $169.10  
  Purchase #5 $95.70   13.352%   $108.4779   $108.48   $108.50   $108.50  
  Purchase #6 $22.25   7.672%   $23.957   $23.96   $23.95   $24.00  
  Purchase #7 $93.27   10.687%   $103.2378   $103.24   $103.25   $103.20  
  7 purchase totals = $876.24       $958.2578   $958.26   $958.25   $958.30