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 $228.63   11.856%   $255.7364   $255.74   $255.75   $255.70  
  Purchase #2 $74.92   11.813%   $83.7703   $83.77   $83.75   $83.80  
  Purchase #3 $249.80   11.293%   $278.0099   $278.01   $278.00   $278.00  
  Purchase #4 $186.55   8.108%   $201.6755   $201.68   $201.70   $201.70  
  Purchase #5 $181.95   5.505%   $191.9663   $191.97   $191.95   $192.00  
  Purchase #6 $195.72   5.256%   $206.007   $206.01   $206.00   $206.00  
  Purchase #7 $69.91   8.193%   $75.6377   $75.64   $75.65   $75.60  
  7 purchase totals = $1,187.48       $1,292.8031   $1,292.82   $1,292.80   $1,292.80