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 $45.34   6.631%   $48.3465   $48.35   $48.35   $48.30  
  Purchase #2 $239.81   3.181%   $247.4384   $247.44   $247.45   $247.40  
  Purchase #3 $95.36   10.463%   $105.3375   $105.34   $105.35   $105.30  
  Purchase #4 $129.89   9.290%   $141.9568   $141.96   $141.95   $142.00  
  Purchase #5 $156.27   6.275%   $166.0759   $166.08   $166.10   $166.10  
  Purchase #6 $148.72   3.863%   $154.4651   $154.47   $154.45   $154.50  
  Purchase #7 $66.77   11.564%   $74.4913   $74.49   $74.50   $74.50  
  7 purchase totals = $882.16       $938.1115   $938.13   $938.15   $938.10