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 $98.71   8.133%   $106.7381   $106.74   $106.75   $106.70  
  Purchase #2 $201.50   13.661%   $229.0269   $229.03   $229.05   $229.00  
  Purchase #3 $72.97   6.381%   $77.6262   $77.63   $77.65   $77.60  
  Purchase #4 $241.86   5.264%   $254.5915   $254.59   $254.60   $254.60  
  Purchase #5 $120.80   13.336%   $136.9099   $136.91   $136.90   $136.90  
  Purchase #6 $173.72   10.176%   $191.3977   $191.40   $191.40   $191.40  
  Purchase #7 $10.38   8.719%   $11.285   $11.29   $11.30   $11.30  
  7 purchase totals = $919.94       $1,007.5753   $1,007.59   $1,007.65   $1,007.50