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 $227.69   11.195%   $253.1799   $253.18   $253.20   $253.20  
  Purchase #2 $179.39   4.633%   $187.7011   $187.70   $187.70   $187.70  
  Purchase #3 $242.62   4.743%   $254.1275   $254.13   $254.15   $254.10  
  Purchase #4 $238.52   13.593%   $270.942   $270.94   $270.95   $270.90  
  Purchase #5 $115.57   8.157%   $124.997   $125.00   $125.00   $125.00  
  Purchase #6 $180.87   5.547%   $190.9029   $190.90   $190.90   $190.90  
  Purchase #7 $54.58   10.577%   $60.3529   $60.35   $60.35   $60.40  
  7 purchase totals = $1,239.24       $1,342.2033   $1,342.20   $1,342.25   $1,342.20