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 $232.62   13.725%   $264.5471   $264.55   $264.55   $264.50  
  Purchase #2 $39.66   11.296%   $44.14   $44.14   $44.15   $44.10  
  Purchase #3 $104.62   3.859%   $108.6573   $108.66   $108.65   $108.70  
  Purchase #4 $123.40   8.606%   $134.0198   $134.02   $134.00   $134.00  
  Purchase #5 $188.74   13.117%   $213.497   $213.50   $213.50   $213.50  
  Purchase #6 $187.89   10.526%   $207.6673   $207.67   $207.65   $207.70  
  Purchase #7 $94.91   8.242%   $102.7325   $102.73   $102.75   $102.70  
  7 purchase totals = $971.84       $1,075.2610   $1,075.27   $1,075.25   $1,075.20