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 $118.32   6.670%   $126.2119   $126.21   $126.20   $126.20  
  Purchase #2 $183.92   12.371%   $206.6727   $206.67   $206.65   $206.70  
  Purchase #3 $106.75   3.284%   $110.2557   $110.26   $110.25   $110.30  
  Purchase #4 $226.65   6.644%   $241.7086   $241.71   $241.70   $241.70  
  Purchase #5 $95.77   9.608%   $104.9716   $104.97   $104.95   $105.00  
  Purchase #6 $8.75   7.206%   $9.3805   $9.38   $9.40   $9.40  
  Purchase #7 $233.92   12.414%   $262.9588   $262.96   $262.95   $263.00  
  7 purchase totals = $974.08       $1,062.1598   $1,062.16   $1,062.10   $1,062.30