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 $64.53   8.588%   $70.0718   $70.07   $70.05   $70.10  
  Purchase #2 $213.94   9.336%   $233.9134   $233.91   $233.90   $233.90  
  Purchase #3 $33.97   5.186%   $35.7317   $35.73   $35.75   $35.70  
  Purchase #4 $245.57   9.472%   $268.8304   $268.83   $268.85   $268.80  
  Purchase #5 $207.49   3.770%   $215.3124   $215.31   $215.30   $215.30  
  Purchase #6 $118.31   3.463%   $122.4071   $122.41   $122.40   $122.40  
  Purchase #7 $115.62   12.616%   $130.2066   $130.21   $130.20   $130.20  
  7 purchase totals = $999.43       $1,076.4734   $1,076.47   $1,076.45   $1,076.40