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 $23.39   12.527%   $26.3201   $26.32   $26.30   $26.30  
  Purchase #2 $239.99   5.137%   $252.3183   $252.32   $252.30   $252.30  
  Purchase #3 $46.56   12.737%   $52.4903   $52.49   $52.50   $52.50  
  Purchase #4 $143.61   11.405%   $159.9887   $159.99   $160.00   $160.00  
  Purchase #5 $102.83   5.361%   $108.3427   $108.34   $108.35   $108.30  
  Purchase #6 $148.81   12.452%   $167.3398   $167.34   $167.35   $167.30  
  Purchase #7 $219.40   10.543%   $242.5313   $242.53   $242.55   $242.50  
  7 purchase totals = $924.59       $1,009.3312   $1,009.33   $1,009.35   $1,009.20