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 $60.51   4.872%   $63.458   $63.46   $63.45   $63.50  
  Purchase #2 $152.69   8.352%   $165.4427   $165.44   $165.45   $165.40  
  Purchase #3 $196.69   9.264%   $214.9114   $214.91   $214.90   $214.90  
  Purchase #4 $169.94   8.525%   $184.4274   $184.43   $184.45   $184.40  
  Purchase #5 $249.35   11.521%   $278.0776   $278.08   $278.10   $278.10  
  Purchase #6 $66.83   9.104%   $72.9142   $72.91   $72.90   $72.90  
  Purchase #7 $236.99   5.494%   $250.0102   $250.01   $250.00   $250.00  
  7 purchase totals = $1,133.00       $1,229.2415   $1,229.24   $1,229.25   $1,229.20