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 $222.44   13.104%   $251.5885   $251.59   $251.60   $251.60  
  Purchase #2 $102.42   8.512%   $111.138   $111.14   $111.15   $111.10  
  Purchase #3 $174.69   11.582%   $194.9226   $194.92   $194.90   $194.90  
  Purchase #4 $239.95   7.108%   $257.0056   $257.01   $257.00   $257.00  
  Purchase #5 $71.78   6.236%   $76.2562   $76.26   $76.25   $76.30  
  Purchase #6 $194.55   5.791%   $205.8164   $205.82   $205.80   $205.80  
  Purchase #7 $100.64   4.520%   $105.1889   $105.19   $105.20   $105.20  
  7 purchase totals = $1,106.47       $1,201.9162   $1,201.93   $1,201.90   $1,201.90