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 $23.41   13.345%   $26.5341   $26.53   $26.55   $26.50  
  Purchase #2 $149.33   10.804%   $165.4636   $165.46   $165.45   $165.50  
  Purchase #3 $13.64   6.650%   $14.5471   $14.55   $14.55   $14.50  
  Purchase #4 $203.25   10.353%   $224.2925   $224.29   $224.30   $224.30  
  Purchase #5 $201.87   12.404%   $226.91   $226.91   $226.90   $226.90  
  Purchase #6 $47.30   5.461%   $49.8831   $49.88   $49.90   $49.90  
  Purchase #7 $110.30   13.664%   $125.3714   $125.37   $125.35   $125.40  
  7 purchase totals = $749.10       $833.0018   $832.99   $833.00   $833.00