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 $33.88   8.119%   $36.6307   $36.63   $36.65   $36.60  
  Purchase #2 $218.27   10.847%   $241.9457   $241.95   $241.95   $241.90  
  Purchase #3 $86.92   9.588%   $95.2539   $95.25   $95.25   $95.30  
  Purchase #4 $198.88   12.267%   $223.2766   $223.28   $223.30   $223.30  
  Purchase #5 $123.31   7.378%   $132.4078   $132.41   $132.40   $132.40  
  Purchase #6 $122.30   12.744%   $137.8859   $137.89   $137.90   $137.90  
  Purchase #7 $7.70   13.372%   $8.7296   $8.73   $8.75   $8.70  
  7 purchase totals = $791.26       $876.1302   $876.14   $876.20   $876.10