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 $63.40   9.291%   $69.2905   $69.29   $69.30   $69.30  
  Purchase #2 $212.67   4.270%   $221.751   $221.75   $221.75   $221.80  
  Purchase #3 $206.27   4.864%   $216.303   $216.30   $216.30   $216.30  
  Purchase #4 $119.99   3.420%   $124.0937   $124.09   $124.10   $124.10  
  Purchase #5 $221.51   8.785%   $240.9697   $240.97   $240.95   $241.00  
  Purchase #6 $216.67   4.508%   $226.4375   $226.44   $226.45   $226.40  
  Purchase #7 $119.49   13.114%   $135.1599   $135.16   $135.15   $135.20  
  7 purchase totals = $1,160.00       $1,234.0053   $1,234.00   $1,234.00   $1,234.10