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 $220.96   5.836%   $233.8552   $233.86   $233.85   $233.90  
  Purchase #2 $193.93   4.337%   $202.3407   $202.34   $202.35   $202.30  
  Purchase #3 $109.59   6.828%   $117.0728   $117.07   $117.05   $117.10  
  Purchase #4 $223.88   5.223%   $235.5733   $235.57   $235.55   $235.60  
  Purchase #5 $228.30   13.753%   $259.6981   $259.70   $259.70   $259.70  
  Purchase #6 $129.55   13.763%   $147.38   $147.38   $147.40   $147.40  
  Purchase #7 $218.43   13.721%   $248.4008   $248.40   $248.40   $248.40  
  7 purchase totals = $1,324.64       $1,444.3209   $1,444.32   $1,444.30   $1,444.40