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 $241.68   4.580%   $252.7489   $252.75   $252.75   $252.70  
  Purchase #2 $126.62   3.267%   $130.7567   $130.76   $130.75   $130.80  
  Purchase #3 $238.34   3.521%   $246.732   $246.73   $246.75   $246.70  
  Purchase #4 $71.86   4.126%   $74.8249   $74.82   $74.80   $74.80  
  Purchase #5 $166.47   5.835%   $176.1835   $176.18   $176.20   $176.20  
  Purchase #6 $26.51   5.435%   $27.9508   $27.95   $27.95   $28.00  
  Purchase #7 $121.79   11.191%   $135.4195   $135.42   $135.40   $135.40  
  7 purchase totals = $993.27       $1,044.6163   $1,044.61   $1,044.60   $1,044.60