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 $216.57   8.527%   $235.0369   $235.04   $235.05   $235.00  
  Purchase #2 $243.86   9.822%   $267.8119   $267.81   $267.80   $267.80  
  Purchase #3 $167.64   9.321%   $183.2657   $183.27   $183.25   $183.30  
  Purchase #4 $195.76   9.238%   $213.8443   $213.84   $213.85   $213.80  
  Purchase #5 $49.66   13.462%   $56.3452   $56.35   $56.35   $56.30  
  Purchase #6 $144.41   12.131%   $161.9284   $161.93   $161.95   $161.90  
  Purchase #7 $63.36   13.195%   $71.7204   $71.72   $71.70   $71.70  
  7 purchase totals = $1,081.26       $1,189.9528   $1,189.96   $1,189.95   $1,189.80