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 $224.27   8.243%   $242.7566   $242.76   $242.75   $242.80  
  Purchase #2 $224.38   10.748%   $248.4964   $248.50   $248.50   $248.50  
  Purchase #3 $126.93   6.761%   $135.5117   $135.51   $135.50   $135.50  
  Purchase #4 $24.74   9.510%   $27.0928   $27.09   $27.10   $27.10  
  Purchase #5 $211.58   7.867%   $228.225   $228.23   $228.25   $228.20  
  Purchase #6 $101.53   6.380%   $108.0076   $108.01   $108.00   $108.00  
  Purchase #7 $73.77   9.296%   $80.6277   $80.63   $80.65   $80.60  
  7 purchase totals = $987.20       $1,070.7178   $1,070.73   $1,070.75   $1,070.70