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 $119.97   3.248%   $123.8666   $123.87   $123.85   $123.90  
  Purchase #2 $56.58   7.758%   $60.9695   $60.97   $60.95   $61.00  
  Purchase #3 $174.47   11.332%   $194.2409   $194.24   $194.25   $194.20  
  Purchase #4 $103.70   7.864%   $111.855   $111.86   $111.85   $111.90  
  Purchase #5 $154.37   4.712%   $161.6439   $161.64   $161.65   $161.60  
  Purchase #6 $238.35   6.253%   $253.254   $253.25   $253.25   $253.30  
  Purchase #7 $211.85   10.812%   $234.7552   $234.76   $234.75   $234.80  
  7 purchase totals = $1,059.29       $1,140.5851   $1,140.59   $1,140.55   $1,140.70