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 $23.59   11.722%   $26.3552   $26.36   $26.35   $26.40  
  Purchase #2 $190.92   3.321%   $197.2605   $197.26   $197.25   $197.30  
  Purchase #3 $183.74   7.261%   $197.0814   $197.08   $197.10   $197.10  
  Purchase #4 $67.57   3.771%   $70.1181   $70.12   $70.10   $70.10  
  Purchase #5 $60.88   12.714%   $68.6203   $68.62   $68.60   $68.60  
  Purchase #6 $200.71   7.220%   $215.2013   $215.20   $215.20   $215.20  
  Purchase #7 $35.76   9.102%   $39.0149   $39.01   $39.00   $39.00  
  7 purchase totals = $763.17       $813.6517   $813.65   $813.60   $813.70