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 $219.61   3.132%   $226.4882   $226.49   $226.50   $226.50  
  Purchase #2 $33.66   7.728%   $36.2612   $36.26   $36.25   $36.30  
  Purchase #3 $41.63   3.474%   $43.0762   $43.08   $43.10   $43.10  
  Purchase #4 $60.56   10.728%   $67.0569   $67.06   $67.05   $67.10  
  Purchase #5 $8.32   5.433%   $8.772   $8.77   $8.75   $8.80  
  Purchase #6 $25.74   3.832%   $26.7264   $26.73   $26.75   $26.70  
  Purchase #7 $57.48   13.211%   $65.0737   $65.07   $65.05   $65.10  
  7 purchase totals = $447.00       $473.4546   $473.46   $473.45   $473.60