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 $85.52   11.853%   $95.6567   $95.66   $95.65   $95.70  
  Purchase #2 $52.82   9.208%   $57.6837   $57.68   $57.70   $57.70  
  Purchase #3 $125.70   4.707%   $131.6167   $131.62   $131.60   $131.60  
  Purchase #4 $142.82   10.569%   $157.9146   $157.91   $157.90   $157.90  
  Purchase #5 $142.88   4.392%   $149.1553   $149.16   $149.15   $149.20  
  Purchase #6 $65.90   10.701%   $72.952   $72.95   $72.95   $73.00  
  Purchase #7 $227.91   13.660%   $259.0425   $259.04   $259.05   $259.00  
  7 purchase totals = $843.55       $924.0215   $924.02   $924.00   $924.10