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 $88.98   5.542%   $93.9113   $93.91   $93.90   $93.90  
  Purchase #2 $12.57   5.450%   $13.2551   $13.26   $13.25   $13.30  
  Purchase #3 $186.57   5.551%   $196.9265   $196.93   $196.95   $196.90  
  Purchase #4 $117.33   7.257%   $125.8446   $125.84   $125.85   $125.80  
  Purchase #5 $166.39   13.750%   $189.2686   $189.27   $189.25   $189.30  
  Purchase #6 $110.38   4.808%   $115.6871   $115.69   $115.70   $115.70  
  Purchase #7 $161.76   12.466%   $181.925   $181.93   $181.95   $181.90  
  7 purchase totals = $843.98       $916.8182   $916.83   $916.85   $916.80