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 $241.50   12.491%   $271.6658   $271.67   $271.65   $271.70  
  Purchase #2 $236.39   8.551%   $256.6037   $256.60   $256.60   $256.60  
  Purchase #3 $205.72   10.188%   $226.6788   $226.68   $226.70   $226.70  
  Purchase #4 $63.56   6.353%   $67.598   $67.60   $67.60   $67.60  
  Purchase #5 $133.58   11.263%   $148.6251   $148.63   $148.65   $148.60  
  Purchase #6 $109.93   3.739%   $114.0403   $114.04   $114.05   $114.00  
  Purchase #7 $84.81   13.808%   $96.5206   $96.52   $96.50   $96.50  
  7 purchase totals = $1,075.49       $1,181.7323   $1,181.74   $1,181.75   $1,181.70