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 $43.81   13.556%   $49.7489   $49.75   $49.75   $49.70  
  Purchase #2 $98.74   8.846%   $107.4745   $107.47   $107.45   $107.50  
  Purchase #3 $13.53   7.263%   $14.5127   $14.51   $14.50   $14.50  
  Purchase #4 $161.67   3.740%   $167.7165   $167.72   $167.70   $167.70  
  Purchase #5 $222.97   8.141%   $241.122   $241.12   $241.10   $241.10  
  Purchase #6 $177.35   4.711%   $185.705   $185.71   $185.70   $185.70  
  Purchase #7 $165.87   7.173%   $177.7679   $177.77   $177.75   $177.80  
  7 purchase totals = $883.94       $944.0475   $944.05   $943.95   $944.00