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 $112.53   5.358%   $118.5594   $118.56   $118.55   $118.60  
  Purchase #2 $196.59   11.139%   $218.4882   $218.49   $218.50   $218.50  
  Purchase #3 $143.74   13.618%   $163.3145   $163.31   $163.30   $163.30  
  Purchase #4 $157.53   7.697%   $169.6551   $169.66   $169.65   $169.70  
  Purchase #5 $239.35   12.752%   $269.8719   $269.87   $269.85   $269.90  
  Purchase #6 $247.98   4.630%   $259.4615   $259.46   $259.45   $259.50  
  Purchase #7 $42.26   11.679%   $47.1955   $47.20   $47.20   $47.20  
  7 purchase totals = $1,139.98       $1,246.5461   $1,246.55   $1,246.50   $1,246.70