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 $126.55   11.602%   $141.2323   $141.23   $141.25   $141.20  
  Purchase #2 $230.91   13.632%   $262.3877   $262.39   $262.40   $262.40  
  Purchase #3 $195.49   3.843%   $203.0027   $203.00   $203.00   $203.00  
  Purchase #4 $231.29   3.409%   $239.1747   $239.17   $239.15   $239.20  
  Purchase #5 $147.98   6.228%   $157.1962   $157.20   $157.20   $157.20  
  Purchase #6 $39.82   3.718%   $41.3005   $41.30   $41.30   $41.30  
  Purchase #7 $83.70   4.294%   $87.2941   $87.29   $87.30   $87.30  
  7 purchase totals = $1,055.74       $1,131.5882   $1,131.58   $1,131.60   $1,131.60