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 $104.43   13.264%   $118.2816   $118.28   $118.30   $118.30  
  Purchase #2 $114.46   10.153%   $126.0811   $126.08   $126.10   $126.10  
  Purchase #3 $87.44   10.457%   $96.5836   $96.58   $96.60   $96.60  
  Purchase #4 $115.65   13.376%   $131.1193   $131.12   $131.10   $131.10  
  Purchase #5 $224.43   10.461%   $247.9076   $247.91   $247.90   $247.90  
  Purchase #6 $8.31   9.725%   $9.1181   $9.12   $9.10   $9.10  
  Purchase #7 $248.98   6.724%   $265.7214   $265.72   $265.70   $265.70  
  7 purchase totals = $903.70       $994.8127   $994.81   $994.80   $994.80