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 $103.94   5.613%   $109.7742   $109.77   $109.75   $109.80  
  Purchase #2 $150.83   3.729%   $156.4545   $156.45   $156.45   $156.50  
  Purchase #3 $23.31   11.503%   $25.9913   $25.99   $26.00   $26.00  
  Purchase #4 $245.57   3.800%   $254.9017   $254.90   $254.90   $254.90  
  Purchase #5 $120.60   12.872%   $136.1236   $136.12   $136.10   $136.10  
  Purchase #6 $86.94   5.803%   $91.9851   $91.99   $92.00   $92.00  
  Purchase #7 $56.83   3.105%   $58.5946   $58.59   $58.60   $58.60  
  7 purchase totals = $788.02       $833.8250   $833.81   $833.80   $833.90