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 $75.47   12.224%   $84.6955   $84.70   $84.70   $84.70  
  Purchase #2 $246.70   9.242%   $269.5   $269.50   $269.50   $269.50  
  Purchase #3 $182.91   4.730%   $191.5616   $191.56   $191.55   $191.60  
  Purchase #4 $45.51   11.821%   $50.8897   $50.89   $50.90   $50.90  
  Purchase #5 $161.67   10.661%   $178.9056   $178.91   $178.90   $178.90  
  Purchase #6 $129.38   12.422%   $145.4516   $145.45   $145.45   $145.50  
  Purchase #7 $97.81   9.256%   $106.8633   $106.86   $106.85   $106.90  
  7 purchase totals = $939.45       $1,027.8673   $1,027.87   $1,027.85   $1,028.00