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 $46.98   5.534%   $49.5799   $49.58   $49.60   $49.60  
  Purchase #2 $121.97   9.243%   $133.2437   $133.24   $133.25   $133.20  
  Purchase #3 $5.74   9.326%   $6.2753   $6.28   $6.30   $6.30  
  Purchase #4 $33.73   5.431%   $35.5619   $35.56   $35.55   $35.60  
  Purchase #5 $35.35   11.213%   $39.3138   $39.31   $39.30   $39.30  
  Purchase #6 $174.72   6.144%   $185.4548   $185.45   $185.45   $185.50  
  Purchase #7 $237.87   7.139%   $254.8515   $254.85   $254.85   $254.90  
  7 purchase totals = $656.36       $704.2809   $704.27   $704.30   $704.40