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 $55.56   10.704%   $61.5071   $61.51   $61.50   $61.50  
  Purchase #2 $132.91   9.618%   $145.6933   $145.69   $145.70   $145.70  
  Purchase #3 $109.69   4.832%   $114.9902   $114.99   $115.00   $115.00  
  Purchase #4 $88.77   7.367%   $95.3097   $95.31   $95.30   $95.30  
  Purchase #5 $90.26   10.290%   $99.5478   $99.55   $99.55   $99.50  
  Purchase #6 $164.35   6.175%   $174.4986   $174.50   $174.50   $174.50  
  Purchase #7 $135.40   7.618%   $145.7148   $145.71   $145.70   $145.70  
  7 purchase totals = $776.94       $837.2615   $837.26   $837.25   $837.20