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 $227.29   8.504%   $246.6187   $246.62   $246.60   $246.60  
  Purchase #2 $134.93   12.674%   $152.031   $152.03   $152.05   $152.00  
  Purchase #3 $18.46   12.208%   $20.7136   $20.71   $20.70   $20.70  
  Purchase #4 $22.80   8.452%   $24.7271   $24.73   $24.75   $24.70  
  Purchase #5 $26.86   8.759%   $29.2127   $29.21   $29.20   $29.20  
  Purchase #6 $137.70   8.691%   $149.6675   $149.67   $149.65   $149.70  
  Purchase #7 $230.59   12.844%   $260.207   $260.21   $260.20   $260.20  
  7 purchase totals = $798.63       $883.1776   $883.18   $883.15   $883.10