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 $52.82   13.268%   $59.8282   $59.83   $59.85   $59.80  
  Purchase #2 $109.27   9.619%   $119.7807   $119.78   $119.80   $119.80  
  Purchase #3 $175.42   12.155%   $196.7423   $196.74   $196.75   $196.70  
  Purchase #4 $166.26   9.446%   $181.9649   $181.96   $181.95   $182.00  
  Purchase #5 $207.41   8.207%   $224.4321   $224.43   $224.45   $224.40  
  Purchase #6 $94.36   3.808%   $97.9532   $97.95   $97.95   $98.00  
  Purchase #7 $158.52   4.362%   $165.4346   $165.43   $165.45   $165.40  
  7 purchase totals = $964.06       $1,046.1360   $1,046.12   $1,046.20   $1,046.10