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 $124.85   5.750%   $132.0289   $132.03   $132.05   $132.00  
  Purchase #2 $78.57   8.209%   $85.0198   $85.02   $85.00   $85.00  
  Purchase #3 $181.53   5.596%   $191.6884   $191.69   $191.70   $191.70  
  Purchase #4 $28.67   7.279%   $30.7569   $30.76   $30.75   $30.80  
  Purchase #5 $70.87   9.423%   $77.5481   $77.55   $77.55   $77.50  
  Purchase #6 $144.48   8.260%   $156.414   $156.41   $156.40   $156.40  
  Purchase #7 $77.65   4.497%   $81.1419   $81.14   $81.15   $81.10  
  7 purchase totals = $706.62       $754.5980   $754.60   $754.60   $754.50