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 $206.82   6.822%   $220.9293   $220.93   $220.95   $220.90  
  Purchase #2 $8.25   7.763%   $8.8904   $8.89   $8.90   $8.90  
  Purchase #3 $61.61   13.830%   $70.1307   $70.13   $70.15   $70.10  
  Purchase #4 $247.93   7.569%   $266.6958   $266.70   $266.70   $266.70  
  Purchase #5 $201.37   11.317%   $224.159   $224.16   $224.15   $224.20  
  Purchase #6 $208.30   12.160%   $233.6293   $233.63   $233.65   $233.60  
  Purchase #7 $217.96   5.702%   $230.3881   $230.39   $230.40   $230.40  
  7 purchase totals = $1,152.24       $1,254.8226   $1,254.83   $1,254.90   $1,254.80