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 $185.38   12.716%   $208.9529   $208.95   $208.95   $209.00  
  Purchase #2 $25.91   3.348%   $26.7775   $26.78   $26.80   $26.80  
  Purchase #3 $58.90   5.607%   $62.2025   $62.20   $62.20   $62.20  
  Purchase #4 $181.76   10.264%   $200.4158   $200.42   $200.40   $200.40  
  Purchase #5 $105.78   8.777%   $115.0643   $115.06   $115.05   $115.10  
  Purchase #6 $239.73   12.437%   $269.5452   $269.55   $269.55   $269.50  
  Purchase #7 $151.39   9.296%   $165.4632   $165.46   $165.45   $165.50  
  7 purchase totals = $948.85       $1,048.4214   $1,048.42   $1,048.40   $1,048.50