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 $92.87   5.193%   $97.6927   $97.69   $97.70   $97.70  
  Purchase #2 $10.70   6.521%   $11.3977   $11.40   $11.40   $11.40  
  Purchase #3 $82.88   5.559%   $87.4873   $87.49   $87.50   $87.50  
  Purchase #4 $63.47   6.179%   $67.3918   $67.39   $67.40   $67.40  
  Purchase #5 $118.42   5.140%   $124.5068   $124.51   $124.50   $124.50  
  Purchase #6 $60.84   7.835%   $65.6068   $65.61   $65.60   $65.60  
  Purchase #7 $53.69   9.146%   $58.6005   $58.60   $58.60   $58.60  
  7 purchase totals = $482.87       $512.6836   $512.69   $512.70   $512.70