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 $204.81   8.406%   $222.0263   $222.03   $222.05   $222.00  
  Purchase #2 $30.79   11.827%   $34.4315   $34.43   $34.45   $34.40  
  Purchase #3 $241.61   6.399%   $257.0706   $257.07   $257.05   $257.10  
  Purchase #4 $25.99   13.492%   $29.4966   $29.50   $29.50   $29.50  
  Purchase #5 $87.67   12.128%   $98.3026   $98.30   $98.30   $98.30  
  Purchase #6 $151.60   6.788%   $161.8906   $161.89   $161.90   $161.90  
  Purchase #7 $234.94   9.314%   $256.8223   $256.82   $256.80   $256.80  
  7 purchase totals = $977.41       $1,060.0405   $1,060.04   $1,060.05   $1,060.00