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 $114.86   8.420%   $124.5312   $124.53   $124.55   $124.50  
  Purchase #2 $160.70   4.316%   $167.6358   $167.64   $167.65   $167.60  
  Purchase #3 $210.36   8.127%   $227.456   $227.46   $227.45   $227.50  
  Purchase #4 $248.30   3.137%   $256.0892   $256.09   $256.10   $256.10  
  Purchase #5 $124.99   8.407%   $135.4979   $135.50   $135.50   $135.50  
  Purchase #6 $167.59   4.760%   $175.5673   $175.57   $175.55   $175.60  
  Purchase #7 $199.80   13.288%   $226.3494   $226.35   $226.35   $226.30  
  7 purchase totals = $1,226.60       $1,313.1268   $1,313.14   $1,313.15   $1,313.10