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 $173.70   10.378%   $191.7266   $191.73   $191.75   $191.70  
  Purchase #2 $61.53   9.139%   $67.1532   $67.15   $67.15   $67.20  
  Purchase #3 $54.80   10.461%   $60.5326   $60.53   $60.55   $60.50  
  Purchase #4 $81.95   6.382%   $87.18   $87.18   $87.20   $87.20  
  Purchase #5 $206.81   12.455%   $232.5682   $232.57   $232.55   $232.60  
  Purchase #6 $75.90   7.577%   $81.6509   $81.65   $81.65   $81.70  
  Purchase #7 $28.25   8.747%   $30.721   $30.72   $30.70   $30.70  
  7 purchase totals = $682.94       $751.5325   $751.53   $751.55   $751.60