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 $77.49   13.859%   $88.2293   $88.23   $88.25   $88.20  
  Purchase #2 $244.38   8.857%   $266.0247   $266.02   $266.00   $266.00  
  Purchase #3 $46.76   11.726%   $52.2431   $52.24   $52.25   $52.20  
  Purchase #4 $173.83   4.520%   $181.6871   $181.69   $181.70   $181.70  
  Purchase #5 $246.50   8.526%   $267.5166   $267.52   $267.50   $267.50  
  Purchase #6 $185.25   5.165%   $194.8182   $194.82   $194.80   $194.80  
  Purchase #7 $113.49   7.238%   $121.7044   $121.70   $121.70   $121.70  
  7 purchase totals = $1,087.70       $1,172.2234   $1,172.22   $1,172.20   $1,172.10