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 $211.64   5.616%   $223.5257   $223.53   $223.55   $223.50  
  Purchase #2 $171.91   6.291%   $182.7249   $182.72   $182.70   $182.70  
  Purchase #3 $24.80   5.234%   $26.098   $26.10   $26.10   $26.10  
  Purchase #4 $61.44   11.216%   $68.3311   $68.33   $68.35   $68.30  
  Purchase #5 $231.85   10.197%   $255.4917   $255.49   $255.50   $255.50  
  Purchase #6 $108.56   5.367%   $114.3864   $114.39   $114.40   $114.40  
  Purchase #7 $121.93   8.263%   $132.0051   $132.01   $132.00   $132.00  
  7 purchase totals = $932.13       $1,002.5629   $1,002.57   $1,002.60   $1,002.50