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 $176.68   3.688%   $183.196   $183.20   $183.20   $183.20  
  Purchase #2 $141.60   10.786%   $156.873   $156.87   $156.85   $156.90  
  Purchase #3 $139.59   5.472%   $147.2284   $147.23   $147.25   $147.20  
  Purchase #4 $204.73   8.795%   $222.736   $222.74   $222.75   $222.70  
  Purchase #5 $83.41   12.744%   $94.0398   $94.04   $94.05   $94.00  
  Purchase #6 $23.59   10.688%   $26.1113   $26.11   $26.10   $26.10  
  Purchase #7 $241.41   3.218%   $249.1786   $249.18   $249.20   $249.20  
  7 purchase totals = $1,011.01       $1,079.3631   $1,079.37   $1,079.40   $1,079.30