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 $24.33   10.776%   $26.9518   $26.95   $26.95   $27.00  
  Purchase #2 $201.31   5.128%   $211.6332   $211.63   $211.65   $211.60  
  Purchase #3 $177.43   11.728%   $198.239   $198.24   $198.25   $198.20  
  Purchase #4 $245.71   13.663%   $279.2814   $279.28   $279.30   $279.30  
  Purchase #5 $31.79   9.373%   $34.7697   $34.77   $34.75   $34.80  
  Purchase #6 $215.76   9.144%   $235.4891   $235.49   $235.50   $235.50  
  Purchase #7 $192.61   9.834%   $211.5513   $211.55   $211.55   $211.60  
  7 purchase totals = $1,088.94       $1,197.9155   $1,197.91   $1,197.95   $1,198.00