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 $62.61   10.486%   $69.1753   $69.18   $69.20   $69.20  
  Purchase #2 $51.72   12.528%   $58.1995   $58.20   $58.20   $58.20  
  Purchase #3 $138.89   3.596%   $143.8845   $143.88   $143.90   $143.90  
  Purchase #4 $113.39   3.731%   $117.6206   $117.62   $117.60   $117.60  
  Purchase #5 $63.69   6.424%   $67.7814   $67.78   $67.80   $67.80  
  Purchase #6 $244.43   13.175%   $276.6337   $276.63   $276.65   $276.60  
  Purchase #7 $222.44   4.526%   $232.5076   $232.51   $232.50   $232.50  
  7 purchase totals = $897.17       $965.8026   $965.80   $965.85   $965.80