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 $197.51   13.762%   $224.6913   $224.69   $224.70   $224.70  
  Purchase #2 $200.78   5.548%   $211.9193   $211.92   $211.90   $211.90  
  Purchase #3 $216.63   12.294%   $243.2625   $243.26   $243.25   $243.30  
  Purchase #4 $153.62   13.825%   $174.858   $174.86   $174.85   $174.90  
  Purchase #5 $28.73   7.694%   $30.9405   $30.94   $30.95   $30.90  
  Purchase #6 $206.49   10.425%   $228.0166   $228.02   $228.00   $228.00  
  Purchase #7 $140.87   4.485%   $147.188   $147.19   $147.20   $147.20  
  7 purchase totals = $1,144.63       $1,260.8762   $1,260.88   $1,260.85   $1,260.90