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 $240.94   6.640%   $256.9384   $256.94   $256.95   $256.90  
  Purchase #2 $190.39   6.661%   $203.0719   $203.07   $203.05   $203.10  
  Purchase #3 $58.42   5.249%   $61.4865   $61.49   $61.50   $61.50  
  Purchase #4 $115.66   3.643%   $119.8735   $119.87   $119.85   $119.90  
  Purchase #5 $71.42   4.777%   $74.8317   $74.83   $74.85   $74.80  
  Purchase #6 $164.41   3.354%   $169.9243   $169.92   $169.90   $169.90  
  Purchase #7 $62.99   4.712%   $65.9581   $65.96   $65.95   $66.00  
  7 purchase totals = $904.23       $952.0844   $952.08   $952.05   $952.10