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 $66.55   10.407%   $73.4759   $73.48   $73.50   $73.50  
  Purchase #2 $235.53   7.238%   $252.5777   $252.58   $252.60   $252.60  
  Purchase #3 $67.62   9.403%   $73.9783   $73.98   $74.00   $74.00  
  Purchase #4 $209.55   5.693%   $221.4797   $221.48   $221.50   $221.50  
  Purchase #5 $74.32   9.291%   $81.2251   $81.23   $81.25   $81.20  
  Purchase #6 $205.28   3.439%   $212.3396   $212.34   $212.35   $212.30  
  Purchase #7 $137.93   5.324%   $145.2734   $145.27   $145.25   $145.30  
  7 purchase totals = $996.78       $1,060.3497   $1,060.36   $1,060.45   $1,060.40