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 $61.29   13.706%   $69.6904   $69.69   $69.70   $69.70  
  Purchase #2 $150.28   10.394%   $165.9001   $165.90   $165.90   $165.90  
  Purchase #3 $9.56   3.369%   $9.8821   $9.88   $9.90   $9.90  
  Purchase #4 $55.65   13.809%   $63.3347   $63.33   $63.35   $63.30  
  Purchase #5 $177.73   10.150%   $195.7696   $195.77   $195.75   $195.80  
  Purchase #6 $208.83   13.491%   $237.0033   $237.00   $237.00   $237.00  
  Purchase #7 $104.99   6.433%   $111.744   $111.74   $111.75   $111.70  
  7 purchase totals = $768.33       $853.3242   $853.31   $853.35   $853.30