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 $159.25   13.257%   $180.3618   $180.36   $180.35   $180.40  
  Purchase #2 $249.94   9.611%   $273.9617   $273.96   $273.95   $274.00  
  Purchase #3 $238.47   6.809%   $254.7074   $254.71   $254.70   $254.70  
  Purchase #4 $166.27   3.711%   $172.4403   $172.44   $172.45   $172.40  
  Purchase #5 $166.37   4.845%   $174.4306   $174.43   $174.45   $174.40  
  Purchase #6 $171.98   8.689%   $186.9233   $186.92   $186.90   $186.90  
  Purchase #7 $41.63   11.310%   $46.3384   $46.34   $46.35   $46.30  
  7 purchase totals = $1,193.91       $1,289.1635   $1,289.16   $1,289.15   $1,289.10