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 $205.87   5.814%   $217.8393   $217.84   $217.85   $217.80  
  Purchase #2 $248.37   9.447%   $271.8335   $271.83   $271.85   $271.80  
  Purchase #3 $45.76   13.554%   $51.9623   $51.96   $51.95   $52.00  
  Purchase #4 $114.46   5.691%   $120.9739   $120.97   $120.95   $121.00  
  Purchase #5 $165.85   4.432%   $173.2005   $173.20   $173.20   $173.20  
  Purchase #6 $67.68   4.523%   $70.7412   $70.74   $70.75   $70.70  
  Purchase #7 $151.43   8.488%   $164.2834   $164.28   $164.30   $164.30  
  7 purchase totals = $999.42       $1,070.8341   $1,070.82   $1,070.85   $1,070.80