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 $91.80   3.178%   $94.7174   $94.72   $94.70   $94.70  
  Purchase #2 $240.98   11.458%   $268.5915   $268.59   $268.60   $268.60  
  Purchase #3 $121.64   12.185%   $136.4618   $136.46   $136.45   $136.50  
  Purchase #4 $38.80   7.517%   $41.7166   $41.72   $41.70   $41.70  
  Purchase #5 $198.71   12.397%   $223.3441   $223.34   $223.35   $223.30  
  Purchase #6 $20.76   7.179%   $22.2504   $22.25   $22.25   $22.30  
  Purchase #7 $51.59   9.577%   $56.5308   $56.53   $56.55   $56.50  
  7 purchase totals = $764.28       $843.6126   $843.61   $843.60   $843.60