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 $57.75   12.419%   $64.922   $64.92   $64.90   $64.90  
  Purchase #2 $134.95   11.543%   $150.5273   $150.53   $150.55   $150.50  
  Purchase #3 $67.33   3.764%   $69.8643   $69.86   $69.85   $69.90  
  Purchase #4 $204.55   10.773%   $226.5862   $226.59   $226.60   $226.60  
  Purchase #5 $23.99   9.566%   $26.2849   $26.28   $26.30   $26.30  
  Purchase #6 $236.60   10.330%   $261.0408   $261.04   $261.05   $261.00  
  Purchase #7 $109.71   4.627%   $114.7863   $114.79   $114.80   $114.80  
  7 purchase totals = $834.88       $914.0118   $914.01   $914.05   $914.00