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 $59.68   5.846%   $63.1689   $63.17   $63.15   $63.20  
  Purchase #2 $197.93   6.705%   $211.2012   $211.20   $211.20   $211.20  
  Purchase #3 $194.34   7.273%   $208.4743   $208.47   $208.45   $208.50  
  Purchase #4 $241.31   7.715%   $259.9271   $259.93   $259.95   $259.90  
  Purchase #5 $198.48   3.431%   $205.2898   $205.29   $205.30   $205.30  
  Purchase #6 $169.62   6.401%   $180.4774   $180.48   $180.50   $180.50  
  Purchase #7 $110.39   4.114%   $114.9314   $114.93   $114.95   $114.90  
  7 purchase totals = $1,171.75       $1,243.4701   $1,243.47   $1,243.50   $1,243.50