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 $88.57   5.748%   $93.661   $93.66   $93.65   $93.70  
  Purchase #2 $238.26   4.573%   $249.1556   $249.16   $249.15   $249.20  
  Purchase #3 $182.65   8.150%   $197.536   $197.54   $197.55   $197.50  
  Purchase #4 $150.63   7.333%   $161.6757   $161.68   $161.70   $161.70  
  Purchase #5 $54.40   7.561%   $58.5132   $58.51   $58.50   $58.50  
  Purchase #6 $137.47   6.504%   $146.411   $146.41   $146.40   $146.40  
  Purchase #7 $186.98   3.259%   $193.0737   $193.07   $193.05   $193.10  
  7 purchase totals = $1,038.96       $1,100.0262   $1,100.03   $1,100.00   $1,100.10