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 $172.57   6.731%   $184.1857   $184.19   $184.20   $184.20  
  Purchase #2 $64.75   11.602%   $72.2623   $72.26   $72.25   $72.30  
  Purchase #3 $59.93   7.263%   $64.2827   $64.28   $64.30   $64.30  
  Purchase #4 $233.76   6.492%   $248.9357   $248.94   $248.95   $248.90  
  Purchase #5 $147.76   4.673%   $154.6648   $154.66   $154.65   $154.70  
  Purchase #6 $176.71   11.649%   $197.2949   $197.29   $197.30   $197.30  
  Purchase #7 $98.63   12.135%   $110.5988   $110.60   $110.60   $110.60  
  7 purchase totals = $954.11       $1,032.2249   $1,032.22   $1,032.25   $1,032.30