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 $55.93   7.551%   $60.1533   $60.15   $60.15   $60.20  
  Purchase #2 $225.80   9.740%   $247.7929   $247.79   $247.80   $247.80  
  Purchase #3 $248.92   5.385%   $262.3243   $262.32   $262.30   $262.30  
  Purchase #4 $56.95   3.469%   $58.9256   $58.93   $58.95   $58.90  
  Purchase #5 $58.95   11.242%   $65.5772   $65.58   $65.60   $65.60  
  Purchase #6 $167.82   13.343%   $190.2122   $190.21   $190.20   $190.20  
  Purchase #7 $169.36   11.773%   $189.2988   $189.30   $189.30   $189.30  
  7 purchase totals = $983.73       $1,074.2843   $1,074.28   $1,074.30   $1,074.30