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 $195.47   8.148%   $211.3969   $211.40   $211.40   $211.40  
  Purchase #2 $118.35   7.155%   $126.8179   $126.82   $126.80   $126.80  
  Purchase #3 $242.79   4.433%   $253.5529   $253.55   $253.55   $253.60  
  Purchase #4 $176.93   7.656%   $190.4758   $190.48   $190.50   $190.50  
  Purchase #5 $33.76   8.520%   $36.6364   $36.64   $36.65   $36.60  
  Purchase #6 $118.41   10.233%   $130.5269   $130.53   $130.55   $130.50  
  Purchase #7 $25.29   3.597%   $26.1997   $26.20   $26.20   $26.20  
  7 purchase totals = $911.00       $975.6065   $975.62   $975.65   $975.60