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 $216.34   13.442%   $245.4204   $245.42   $245.40   $245.40  
  Purchase #2 $60.27   10.586%   $66.6502   $66.65   $66.65   $66.70  
  Purchase #3 $173.33   6.265%   $184.1891   $184.19   $184.20   $184.20  
  Purchase #4 $182.57   8.466%   $198.0264   $198.03   $198.05   $198.00  
  Purchase #5 $50.96   3.768%   $52.8802   $52.88   $52.90   $52.90  
  Purchase #6 $176.81   6.632%   $188.536   $188.54   $188.55   $188.50  
  Purchase #7 $54.69   11.295%   $60.8672   $60.87   $60.85   $60.90  
  7 purchase totals = $914.97       $996.5695   $996.58   $996.60   $996.60