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 $85.67   13.303%   $97.0667   $97.07   $97.05   $97.10  
  Purchase #2 $94.39   9.622%   $103.4722   $103.47   $103.45   $103.50  
  Purchase #3 $156.81   5.783%   $165.8783   $165.88   $165.90   $165.90  
  Purchase #4 $51.70   11.206%   $57.4935   $57.49   $57.50   $57.50  
  Purchase #5 $74.58   3.275%   $77.0225   $77.02   $77.00   $77.00  
  Purchase #6 $152.62   8.723%   $165.933   $165.93   $165.95   $165.90  
  Purchase #7 $237.42   5.322%   $250.0555   $250.06   $250.05   $250.10  
  7 purchase totals = $853.19       $916.9217   $916.92   $916.90   $917.00