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 $118.83   3.746%   $123.2814   $123.28   $123.30   $123.30  
  Purchase #2 $238.39   12.129%   $267.3043   $267.30   $267.30   $267.30  
  Purchase #3 $220.73   12.237%   $247.7407   $247.74   $247.75   $247.70  
  Purchase #4 $107.66   11.672%   $120.2261   $120.23   $120.25   $120.20  
  Purchase #5 $200.81   8.636%   $218.152   $218.15   $218.15   $218.20  
  Purchase #6 $228.60   8.635%   $248.3396   $248.34   $248.35   $248.30  
  Purchase #7 $69.40   6.356%   $73.8111   $73.81   $73.80   $73.80  
  7 purchase totals = $1,184.42       $1,298.8552   $1,298.85   $1,298.90   $1,298.80