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 $22.91   5.765%   $24.2308   $24.23   $24.25   $24.20  
  Purchase #2 $57.67   9.250%   $63.0045   $63.00   $63.00   $63.00  
  Purchase #3 $115.96   10.123%   $127.6986   $127.70   $127.70   $127.70  
  Purchase #4 $222.93   8.425%   $241.7119   $241.71   $241.70   $241.70  
  Purchase #5 $102.39   9.239%   $111.8498   $111.85   $111.85   $111.80  
  Purchase #6 $187.51   5.459%   $197.7462   $197.75   $197.75   $197.70  
  Purchase #7 $200.63   5.416%   $211.4961   $211.50   $211.50   $211.50  
  7 purchase totals = $910.00       $977.7379   $977.74   $977.75   $977.60