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 $74.74   6.835%   $79.8485   $79.85   $79.85   $79.80  
  Purchase #2 $79.52   5.408%   $83.8204   $83.82   $83.80   $83.80  
  Purchase #3 $235.45   7.148%   $252.28   $252.28   $252.30   $252.30  
  Purchase #4 $76.47   12.159%   $85.768   $85.77   $85.75   $85.80  
  Purchase #5 $153.61   8.422%   $166.547   $166.55   $166.55   $166.50  
  Purchase #6 $187.86   5.156%   $197.5461   $197.55   $197.55   $197.50  
  Purchase #7 $179.48   3.429%   $185.6344   $185.63   $185.65   $185.60  
  7 purchase totals = $987.13       $1,051.4444   $1,051.45   $1,051.45   $1,051.30