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 $162.76   12.833%   $183.647   $183.65   $183.65   $183.60  
  Purchase #2 $11.50   5.860%   $12.1739   $12.17   $12.15   $12.20  
  Purchase #3 $56.54   10.431%   $62.4377   $62.44   $62.45   $62.40  
  Purchase #4 $97.29   8.409%   $105.4711   $105.47   $105.45   $105.50  
  Purchase #5 $52.61   5.454%   $55.4793   $55.48   $55.50   $55.50  
  Purchase #6 $144.76   11.245%   $161.0383   $161.04   $161.05   $161.00  
  Purchase #7 $246.48   9.462%   $269.8019   $269.80   $269.80   $269.80  
  7 purchase totals = $771.94       $850.0492   $850.05   $850.05   $850.00