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 $56.86   8.817%   $61.8733   $61.87   $61.85   $61.90  
  Purchase #2 $221.48   5.413%   $233.4687   $233.47   $233.45   $233.50  
  Purchase #3 $153.62   8.510%   $166.6931   $166.69   $166.70   $166.70  
  Purchase #4 $114.44   6.341%   $121.6966   $121.70   $121.70   $121.70  
  Purchase #5 $9.25   8.232%   $10.0115   $10.01   $10.00   $10.00  
  Purchase #6 $9.91   7.142%   $10.6178   $10.62   $10.60   $10.60  
  Purchase #7 $24.49   3.416%   $25.3266   $25.33   $25.35   $25.30  
  7 purchase totals = $590.05       $629.6876   $629.69   $629.65   $629.70