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 $53.70   9.774%   $58.9486   $58.95   $58.95   $58.90  
  Purchase #2 $242.83   4.762%   $254.3936   $254.39   $254.40   $254.40  
  Purchase #3 $80.95   6.696%   $86.3704   $86.37   $86.35   $86.40  
  Purchase #4 $166.72   12.679%   $187.8584   $187.86   $187.85   $187.90  
  Purchase #5 $33.86   12.640%   $38.1399   $38.14   $38.15   $38.10  
  Purchase #6 $32.38   9.262%   $35.379   $35.38   $35.40   $35.40  
  Purchase #7 $160.94   3.146%   $166.0032   $166.00   $166.00   $166.00  
  7 purchase totals = $771.38       $827.0931   $827.09   $827.10   $827.10