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 $209.84   11.864%   $234.7354   $234.74   $234.75   $234.70  
  Purchase #2 $113.54   9.429%   $124.2457   $124.25   $124.25   $124.20  
  Purchase #3 $14.49   10.388%   $15.9952   $16.00   $16.00   $16.00  
  Purchase #4 $172.68   3.150%   $178.1194   $178.12   $178.10   $178.10  
  Purchase #5 $36.31   12.812%   $40.962   $40.96   $40.95   $41.00  
  Purchase #6 $221.95   5.262%   $233.629   $233.63   $233.65   $233.60  
  Purchase #7 $228.38   9.563%   $250.22   $250.22   $250.20   $250.20  
  7 purchase totals = $997.19       $1,077.9067   $1,077.92   $1,077.90   $1,077.80