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 $248.88   5.571%   $262.7451   $262.75   $262.75   $262.70  
  Purchase #2 $174.97   5.159%   $183.9967   $184.00   $184.00   $184.00  
  Purchase #3 $9.33   4.754%   $9.7735   $9.77   $9.75   $9.80  
  Purchase #4 $244.82   6.524%   $260.7921   $260.79   $260.80   $260.80  
  Purchase #5 $36.79   8.739%   $40.0051   $40.01   $40.00   $40.00  
  Purchase #6 $160.93   12.211%   $180.5812   $180.58   $180.60   $180.60  
  Purchase #7 $228.62   7.858%   $246.585   $246.59   $246.60   $246.60  
  7 purchase totals = $1,104.34       $1,184.4787   $1,184.49   $1,184.50   $1,184.50