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 $82.82   5.240%   $87.1598   $87.16   $87.15   $87.20  
  Purchase #2 $226.45   8.401%   $245.4741   $245.47   $245.45   $245.50  
  Purchase #3 $109.26   4.183%   $113.8303   $113.83   $113.85   $113.80  
  Purchase #4 $229.72   4.391%   $239.807   $239.81   $239.80   $239.80  
  Purchase #5 $54.58   13.510%   $61.9538   $61.95   $61.95   $62.00  
  Purchase #6 $246.51   12.301%   $276.8332   $276.83   $276.85   $276.80  
  Purchase #7 $160.91   6.857%   $171.9436   $171.94   $171.95   $171.90  
  7 purchase totals = $1,110.25       $1,197.0018   $1,196.99   $1,197.00   $1,197.00