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 $134.59   13.856%   $153.2388   $153.24   $153.25   $153.20  
  Purchase #2 $211.90   7.183%   $227.1208   $227.12   $227.10   $227.10  
  Purchase #3 $16.76   6.746%   $17.8906   $17.89   $17.90   $17.90  
  Purchase #4 $23.63   8.644%   $25.6726   $25.67   $25.65   $25.70  
  Purchase #5 $194.54   3.265%   $200.8917   $200.89   $200.90   $200.90  
  Purchase #6 $11.94   6.682%   $12.7378   $12.74   $12.75   $12.70  
  Purchase #7 $123.95   8.346%   $134.2949   $134.29   $134.30   $134.30  
  7 purchase totals = $717.31       $771.8472   $771.84   $771.85   $771.80