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 $182.76   8.859%   $198.9507   $198.95   $198.95   $199.00  
  Purchase #2 $150.85   3.605%   $156.2881   $156.29   $156.30   $156.30  
  Purchase #3 $247.47   12.458%   $278.2998   $278.30   $278.30   $278.30  
  Purchase #4 $186.69   3.818%   $193.8178   $193.82   $193.80   $193.80  
  Purchase #5 $249.75   10.463%   $275.8813   $275.88   $275.90   $275.90  
  Purchase #6 $119.30   13.180%   $135.0237   $135.02   $135.00   $135.00  
  Purchase #7 $24.65   6.303%   $26.2037   $26.20   $26.20   $26.20  
  7 purchase totals = $1,161.47       $1,264.4651   $1,264.46   $1,264.45   $1,264.50