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 $238.70   10.264%   $263.2002   $263.20   $263.20   $263.20  
  Purchase #2 $127.71   8.499%   $138.5641   $138.56   $138.55   $138.60  
  Purchase #3 $245.50   6.773%   $262.1277   $262.13   $262.15   $262.10  
  Purchase #4 $158.98   11.526%   $177.304   $177.30   $177.30   $177.30  
  Purchase #5 $114.26   5.342%   $120.3638   $120.36   $120.35   $120.40  
  Purchase #6 $116.56   8.110%   $126.013   $126.01   $126.00   $126.00  
  Purchase #7 $112.30   4.842%   $117.7376   $117.74   $117.75   $117.70  
  7 purchase totals = $1,114.01       $1,205.3104   $1,205.30   $1,205.30   $1,205.30