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 $21.87   13.390%   $24.7984   $24.80   $24.80   $24.80  
  Purchase #2 $64.81   6.108%   $68.7686   $68.77   $68.75   $68.80  
  Purchase #3 $241.55   6.230%   $256.5986   $256.60   $256.60   $256.60  
  Purchase #4 $168.85   4.534%   $176.5057   $176.51   $176.50   $176.50  
  Purchase #5 $178.62   7.743%   $192.4505   $192.45   $192.45   $192.50  
  Purchase #6 $58.94   5.269%   $62.0455   $62.05   $62.05   $62.00  
  Purchase #7 $227.77   7.827%   $245.5976   $245.60   $245.60   $245.60  
  7 purchase totals = $962.41       $1,026.7649   $1,026.78   $1,026.75   $1,026.80