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 $71.59   6.661%   $76.3586   $76.36   $76.35   $76.40  
  Purchase #2 $143.29   8.136%   $154.9481   $154.95   $154.95   $154.90  
  Purchase #3 $157.85   13.401%   $179.0035   $179.00   $179.00   $179.00  
  Purchase #4 $23.90   8.622%   $25.9607   $25.96   $25.95   $26.00  
  Purchase #5 $202.71   8.231%   $219.3951   $219.40   $219.40   $219.40  
  Purchase #6 $244.25   11.416%   $272.1336   $272.13   $272.15   $272.10  
  Purchase #7 $90.92   8.524%   $98.67   $98.67   $98.65   $98.70  
  7 purchase totals = $934.51       $1,026.4696   $1,026.47   $1,026.45   $1,026.50