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 $197.87   11.621%   $220.8645   $220.86   $220.85   $220.90  
  Purchase #2 $58.90   7.215%   $63.1496   $63.15   $63.15   $63.10  
  Purchase #3 $60.93   9.144%   $66.5014   $66.50   $66.50   $66.50  
  Purchase #4 $186.91   4.606%   $195.5191   $195.52   $195.50   $195.50  
  Purchase #5 $76.40   12.448%   $85.9103   $85.91   $85.90   $85.90  
  Purchase #6 $181.52   11.581%   $202.5418   $202.54   $202.55   $202.50  
  Purchase #7 $69.26   3.344%   $71.5761   $71.58   $71.60   $71.60  
  7 purchase totals = $831.79       $906.0628   $906.06   $906.05   $906.00