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 $183.63   12.634%   $206.8298   $206.83   $206.85   $206.80  
  Purchase #2 $241.42   4.870%   $253.1772   $253.18   $253.20   $253.20  
  Purchase #3 $73.27   12.174%   $82.1899   $82.19   $82.20   $82.20  
  Purchase #4 $156.67   13.677%   $178.0978   $178.10   $178.10   $178.10  
  Purchase #5 $67.50   3.170%   $69.6398   $69.64   $69.65   $69.60  
  Purchase #6 $121.26   9.391%   $132.6475   $132.65   $132.65   $132.60  
  Purchase #7 $215.37   8.132%   $232.8839   $232.88   $232.90   $232.90  
  7 purchase totals = $1,059.12       $1,155.4659   $1,155.47   $1,155.55   $1,155.40