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 $201.36   3.527%   $208.462   $208.46   $208.45   $208.50  
  Purchase #2 $20.57   12.561%   $23.1538   $23.15   $23.15   $23.20  
  Purchase #3 $53.66   8.376%   $58.1546   $58.15   $58.15   $58.20  
  Purchase #4 $116.29   12.206%   $130.4844   $130.48   $130.50   $130.50  
  Purchase #5 $99.35   11.708%   $110.9819   $110.98   $111.00   $111.00  
  Purchase #6 $219.54   10.300%   $242.1526   $242.15   $242.15   $242.20  
  Purchase #7 $39.57   8.683%   $43.0059   $43.01   $43.00   $43.00  
  7 purchase totals = $750.34       $816.3952   $816.38   $816.40   $816.60