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 $128.27   13.254%   $145.2709   $145.27   $145.25   $145.30  
  Purchase #2 $60.35   10.297%   $66.5642   $66.56   $66.55   $66.60  
  Purchase #3 $218.72   7.385%   $234.8725   $234.87   $234.85   $234.90  
  Purchase #4 $112.82   4.376%   $117.757   $117.76   $117.75   $117.80  
  Purchase #5 $215.53   6.522%   $229.5869   $229.59   $229.60   $229.60  
  Purchase #6 $27.91   6.200%   $29.6404   $29.64   $29.65   $29.60  
  Purchase #7 $58.97   8.393%   $63.9194   $63.92   $63.90   $63.90  
  7 purchase totals = $822.57       $887.6113   $887.61   $887.55   $887.70