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 $206.39   4.595%   $215.8736   $215.87   $215.85   $215.90  
  Purchase #2 $142.88   6.330%   $151.9243   $151.92   $151.90   $151.90  
  Purchase #3 $50.57   3.815%   $52.4992   $52.50   $52.50   $52.50  
  Purchase #4 $16.37   11.560%   $18.2624   $18.26   $18.25   $18.30  
  Purchase #5 $44.99   9.377%   $49.2087   $49.21   $49.20   $49.20  
  Purchase #6 $120.90   7.477%   $129.9397   $129.94   $129.95   $129.90  
  Purchase #7 $75.51   7.845%   $81.4338   $81.43   $81.45   $81.40  
  7 purchase totals = $657.61       $699.1417   $699.13   $699.10   $699.10