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 $246.28   11.659%   $274.9938   $274.99   $275.00   $275.00  
  Purchase #2 $161.75   13.153%   $183.025   $183.03   $183.05   $183.00  
  Purchase #3 $58.61   5.419%   $61.7861   $61.79   $61.80   $61.80  
  Purchase #4 $66.80   4.770%   $69.9864   $69.99   $70.00   $70.00  
  Purchase #5 $248.89   5.692%   $263.0568   $263.06   $263.05   $263.10  
  Purchase #6 $50.65   11.433%   $56.4408   $56.44   $56.45   $56.40  
  Purchase #7 $54.34   8.391%   $58.8997   $58.90   $58.90   $58.90  
  7 purchase totals = $887.32       $968.1886   $968.20   $968.25   $968.20