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 $226.34   9.588%   $248.0415   $248.04   $248.05   $248.00  
  Purchase #2 $40.52   4.642%   $42.4009   $42.40   $42.40   $42.40  
  Purchase #3 $113.78   11.594%   $126.9717   $126.97   $126.95   $127.00  
  Purchase #4 $76.75   3.510%   $79.4439   $79.44   $79.45   $79.40  
  Purchase #5 $46.36   7.600%   $49.8834   $49.88   $49.90   $49.90  
  Purchase #6 $8.25   5.676%   $8.7183   $8.72   $8.70   $8.70  
  Purchase #7 $191.47   3.332%   $197.8498   $197.85   $197.85   $197.80  
  7 purchase totals = $703.47       $753.3095   $753.30   $753.30   $753.20