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 $230.82   7.704%   $248.6024   $248.60   $248.60   $248.60  
  Purchase #2 $164.74   5.786%   $174.2719   $174.27   $174.25   $174.30  
  Purchase #3 $236.31   8.757%   $257.0037   $257.00   $257.00   $257.00  
  Purchase #4 $13.39   10.290%   $14.7678   $14.77   $14.75   $14.80  
  Purchase #5 $150.79   8.621%   $163.7896   $163.79   $163.80   $163.80  
  Purchase #6 $60.68   9.831%   $66.6455   $66.65   $66.65   $66.60  
  Purchase #7 $191.49   4.766%   $200.6164   $200.62   $200.60   $200.60  
  7 purchase totals = $1,048.22       $1,125.6973   $1,125.70   $1,125.65   $1,125.70