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 $236.98   6.324%   $251.9666   $251.97   $251.95   $252.00  
  Purchase #2 $140.31   3.869%   $145.7386   $145.74   $145.75   $145.70  
  Purchase #3 $114.48   11.271%   $127.383   $127.38   $127.40   $127.40  
  Purchase #4 $198.90   6.521%   $211.8703   $211.87   $211.85   $211.90  
  Purchase #5 $192.60   5.639%   $203.4607   $203.46   $203.45   $203.50  
  Purchase #6 $246.67   12.283%   $276.9685   $276.97   $276.95   $277.00  
  Purchase #7 $237.65   5.861%   $251.5787   $251.58   $251.60   $251.60  
  7 purchase totals = $1,367.59       $1,468.9664   $1,468.97   $1,468.95   $1,469.10