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 $184.97   5.609%   $195.345   $195.35   $195.35   $195.30  
  Purchase #2 $244.86   11.683%   $273.467   $273.47   $273.45   $273.50  
  Purchase #3 $48.62   4.779%   $50.9435   $50.94   $50.95   $50.90  
  Purchase #4 $79.56   6.263%   $84.5428   $84.54   $84.55   $84.50  
  Purchase #5 $167.89   4.766%   $175.8916   $175.89   $175.90   $175.90  
  Purchase #6 $38.92   4.183%   $40.548   $40.55   $40.55   $40.50  
  Purchase #7 $158.99   5.708%   $168.0651   $168.07   $168.05   $168.10  
  7 purchase totals = $923.81       $988.8030   $988.81   $988.80   $988.70