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 $248.31   13.773%   $282.5097   $282.51   $282.50   $282.50  
  Purchase #2 $248.62   12.302%   $279.2052   $279.21   $279.20   $279.20  
  Purchase #3 $156.33   4.596%   $163.5149   $163.51   $163.50   $163.50  
  Purchase #4 $246.69   7.132%   $264.2839   $264.28   $264.30   $264.30  
  Purchase #5 $233.88   4.495%   $244.3929   $244.39   $244.40   $244.40  
  Purchase #6 $130.96   3.244%   $135.2083   $135.21   $135.20   $135.20  
  Purchase #7 $73.56   9.233%   $80.3518   $80.35   $80.35   $80.40  
  7 purchase totals = $1,338.35       $1,449.4667   $1,449.46   $1,449.45   $1,449.50