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 $24.47   9.342%   $26.756   $26.76   $26.75   $26.80  
  Purchase #2 $17.89   8.341%   $19.3822   $19.38   $19.40   $19.40  
  Purchase #3 $180.58   3.270%   $186.485   $186.49   $186.50   $186.50  
  Purchase #4 $87.72   8.480%   $95.1587   $95.16   $95.15   $95.20  
  Purchase #5 $219.76   12.700%   $247.6695   $247.67   $247.65   $247.70  
  Purchase #6 $134.43   6.240%   $142.8184   $142.82   $142.80   $142.80  
  Purchase #7 $199.52   8.212%   $215.9046   $215.90   $215.90   $215.90  
  7 purchase totals = $864.37       $934.1744   $934.18   $934.15   $934.30