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 $241.27   4.778%   $252.7979   $252.80   $252.80   $252.80  
  Purchase #2 $158.46   11.608%   $176.854   $176.85   $176.85   $176.90  
  Purchase #3 $248.98   11.339%   $277.2118   $277.21   $277.20   $277.20  
  Purchase #4 $59.94   3.260%   $61.894   $61.89   $61.90   $61.90  
  Purchase #5 $224.45   6.661%   $239.4006   $239.40   $239.40   $239.40  
  Purchase #6 $59.91   6.498%   $63.803   $63.80   $63.80   $63.80  
  Purchase #7 $80.57   7.390%   $86.5241   $86.52   $86.50   $86.50  
  7 purchase totals = $1,073.58       $1,158.4854   $1,158.47   $1,158.45   $1,158.50