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 $206.44   13.849%   $235.0299   $235.03   $235.05   $235.00  
  Purchase #2 $85.46   10.520%   $94.4504   $94.45   $94.45   $94.50  
  Purchase #3 $236.73   12.635%   $266.6408   $266.64   $266.65   $266.60  
  Purchase #4 $92.70   12.531%   $104.3162   $104.32   $104.30   $104.30  
  Purchase #5 $38.69   12.595%   $43.563   $43.56   $43.55   $43.60  
  Purchase #6 $170.75   5.656%   $180.4076   $180.41   $180.40   $180.40  
  Purchase #7 $50.43   9.693%   $55.3182   $55.32   $55.30   $55.30  
  7 purchase totals = $881.20       $979.7261   $979.73   $979.70   $979.70