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 $23.48   13.651%   $26.6853   $26.69   $26.70   $26.70  
  Purchase #2 $121.70   4.328%   $126.9672   $126.97   $126.95   $127.00  
  Purchase #3 $104.68   11.600%   $116.8229   $116.82   $116.80   $116.80  
  Purchase #4 $134.75   3.599%   $139.5997   $139.60   $139.60   $139.60  
  Purchase #5 $245.57   9.804%   $269.6457   $269.65   $269.65   $269.60  
  Purchase #6 $192.88   4.486%   $201.5326   $201.53   $201.55   $201.50  
  Purchase #7 $128.92   9.798%   $141.5516   $141.55   $141.55   $141.60  
  7 purchase totals = $951.98       $1,022.8050   $1,022.81   $1,022.80   $1,022.80