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 $243.84   10.428%   $269.2676   $269.27   $269.25   $269.30  
  Purchase #2 $44.96   4.793%   $47.1149   $47.11   $47.10   $47.10  
  Purchase #3 $26.96   7.865%   $29.0804   $29.08   $29.10   $29.10  
  Purchase #4 $185.63   11.220%   $206.4577   $206.46   $206.45   $206.50  
  Purchase #5 $135.38   11.551%   $151.0177   $151.02   $151.00   $151.00  
  Purchase #6 $220.70   9.156%   $240.9073   $240.91   $240.90   $240.90  
  Purchase #7 $146.56   9.513%   $160.5023   $160.50   $160.50   $160.50  
  7 purchase totals = $1,004.03       $1,104.3479   $1,104.35   $1,104.30   $1,104.40