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 $85.58   11.766%   $95.6493   $95.65   $95.65   $95.60  
  Purchase #2 $220.69   8.277%   $238.9565   $238.96   $238.95   $239.00  
  Purchase #3 $80.44   9.536%   $88.1108   $88.11   $88.10   $88.10  
  Purchase #4 $239.49   5.563%   $252.8128   $252.81   $252.80   $252.80  
  Purchase #5 $21.71   11.559%   $24.2195   $24.22   $24.20   $24.20  
  Purchase #6 $225.49   9.746%   $247.4663   $247.47   $247.45   $247.50  
  Purchase #7 $88.63   10.859%   $98.2543   $98.25   $98.25   $98.30  
  7 purchase totals = $962.03       $1,045.4695   $1,045.47   $1,045.40   $1,045.50