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 $208.72   11.619%   $232.9712   $232.97   $232.95   $233.00  
  Purchase #2 $106.84   11.213%   $118.82   $118.82   $118.80   $118.80  
  Purchase #3 $146.41   13.166%   $165.6863   $165.69   $165.70   $165.70  
  Purchase #4 $105.44   8.422%   $114.3202   $114.32   $114.30   $114.30  
  Purchase #5 $246.74   9.321%   $269.7386   $269.74   $269.75   $269.70  
  Purchase #6 $94.57   10.395%   $104.4006   $104.40   $104.40   $104.40  
  Purchase #7 $175.87   12.212%   $197.3472   $197.35   $197.35   $197.30  
  7 purchase totals = $1,084.59       $1,203.2841   $1,203.29   $1,203.25   $1,203.20