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 $58.59   8.830%   $63.7635   $63.76   $63.75   $63.80  
  Purchase #2 $186.68   9.860%   $205.0866   $205.09   $205.10   $205.10  
  Purchase #3 $204.85   10.570%   $226.5026   $226.50   $226.50   $226.50  
  Purchase #4 $123.86   7.186%   $132.7606   $132.76   $132.75   $132.80  
  Purchase #5 $70.65   12.299%   $79.3392   $79.34   $79.35   $79.30  
  Purchase #6 $184.41   9.666%   $202.2351   $202.24   $202.25   $202.20  
  Purchase #7 $125.54   6.245%   $133.38   $133.38   $133.40   $133.40  
  7 purchase totals = $954.58       $1,043.0676   $1,043.07   $1,043.10   $1,043.10