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 $32.68   13.809%   $37.1928   $37.19   $37.20   $37.20  
  Purchase #2 $237.40   12.391%   $266.8162   $266.82   $266.80   $266.80  
  Purchase #3 $217.44   7.291%   $233.2936   $233.29   $233.30   $233.30  
  Purchase #4 $165.46   4.802%   $173.4054   $173.41   $173.40   $173.40  
  Purchase #5 $24.94   7.583%   $26.8312   $26.83   $26.85   $26.80  
  Purchase #6 $176.55   9.681%   $193.6418   $193.64   $193.65   $193.60  
  Purchase #7 $96.94   8.503%   $105.1828   $105.18   $105.20   $105.20  
  7 purchase totals = $951.41       $1,036.3638   $1,036.36   $1,036.40   $1,036.30