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 $66.99   11.595%   $74.7575   $74.76   $74.75   $74.80  
  Purchase #2 $54.56   13.591%   $61.9752   $61.98   $62.00   $62.00  
  Purchase #3 $37.80   4.244%   $39.4042   $39.40   $39.40   $39.40  
  Purchase #4 $214.58   9.337%   $234.6153   $234.62   $234.60   $234.60  
  Purchase #5 $75.86   4.405%   $79.2016   $79.20   $79.20   $79.20  
  Purchase #6 $120.25   9.662%   $131.8686   $131.87   $131.85   $131.90  
  Purchase #7 $245.34   8.328%   $265.7719   $265.77   $265.75   $265.80  
  7 purchase totals = $815.38       $887.5943   $887.60   $887.55   $887.70