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 $245.45   8.762%   $266.9563   $266.96   $266.95   $267.00  
  Purchase #2 $69.99   4.279%   $72.9849   $72.98   $73.00   $73.00  
  Purchase #3 $148.82   3.819%   $154.5034   $154.50   $154.50   $154.50  
  Purchase #4 $181.96   5.185%   $191.3946   $191.39   $191.40   $191.40  
  Purchase #5 $176.92   11.246%   $196.8164   $196.82   $196.80   $196.80  
  Purchase #6 $192.53   9.834%   $211.4634   $211.46   $211.45   $211.50  
  Purchase #7 $235.96   4.533%   $246.6561   $246.66   $246.65   $246.70  
  7 purchase totals = $1,251.63       $1,340.7751   $1,340.77   $1,340.75   $1,340.90