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 $91.46   5.848%   $96.8086   $96.81   $96.80   $96.80  
  Purchase #2 $183.66   3.273%   $189.6712   $189.67   $189.65   $189.70  
  Purchase #3 $116.75   6.711%   $124.5851   $124.59   $124.60   $124.60  
  Purchase #4 $208.26   12.570%   $234.4383   $234.44   $234.45   $234.40  
  Purchase #5 $43.28   6.277%   $45.9967   $46.00   $46.00   $46.00  
  Purchase #6 $173.48   13.495%   $196.8911   $196.89   $196.90   $196.90  
  Purchase #7 $70.51   7.853%   $76.0472   $76.05   $76.05   $76.00  
  7 purchase totals = $887.40       $964.4382   $964.45   $964.45   $964.40