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 $91.36   5.846%   $96.7009   $96.70   $96.70   $96.70  
  Purchase #2 $140.66   7.715%   $151.5119   $151.51   $151.50   $151.50  
  Purchase #3 $175.48   6.622%   $187.1003   $187.10   $187.10   $187.10  
  Purchase #4 $176.72   5.739%   $186.862   $186.86   $186.85   $186.90  
  Purchase #5 $132.64   4.286%   $138.325   $138.33   $138.35   $138.30  
  Purchase #6 $205.74   10.243%   $226.8139   $226.81   $226.80   $226.80  
  Purchase #7 $239.94   5.407%   $252.9136   $252.91   $252.90   $252.90  
  7 purchase totals = $1,162.54       $1,240.2276   $1,240.22   $1,240.20   $1,240.20