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 $56.81   7.498%   $61.0696   $61.07   $61.05   $61.10  
  Purchase #2 $113.58   8.693%   $123.4535   $123.45   $123.45   $123.50  
  Purchase #3 $108.28   5.697%   $114.4487   $114.45   $114.45   $114.40  
  Purchase #4 $195.30   3.781%   $202.6843   $202.68   $202.70   $202.70  
  Purchase #5 $55.44   9.211%   $60.5466   $60.55   $60.55   $60.50  
  Purchase #6 $180.35   3.519%   $186.6965   $186.70   $186.70   $186.70  
  Purchase #7 $67.89   5.169%   $71.3992   $71.40   $71.40   $71.40  
  7 purchase totals = $777.65       $820.2984   $820.30   $820.30   $820.30