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 $203.47   6.407%   $216.5063   $216.51   $216.50   $216.50  
  Purchase #2 $109.71   6.590%   $116.9399   $116.94   $116.95   $116.90  
  Purchase #3 $212.47   9.687%   $233.052   $233.05   $233.05   $233.10  
  Purchase #4 $109.73   4.247%   $114.3902   $114.39   $114.40   $114.40  
  Purchase #5 $133.49   12.107%   $149.6516   $149.65   $149.65   $149.70  
  Purchase #6 $235.32   11.640%   $262.7112   $262.71   $262.70   $262.70  
  Purchase #7 $217.75   6.354%   $231.5858   $231.59   $231.60   $231.60  
  7 purchase totals = $1,221.94       $1,324.8370   $1,324.84   $1,324.85   $1,324.90