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 $61.27   12.646%   $69.0182   $69.02   $69.00   $69.00  
  Purchase #2 $249.96   9.171%   $272.8838   $272.88   $272.90   $272.90  
  Purchase #3 $154.87   8.418%   $167.907   $167.91   $167.90   $167.90  
  Purchase #4 $51.33   7.321%   $55.0879   $55.09   $55.10   $55.10  
  Purchase #5 $16.30   4.500%   $17.0335   $17.03   $17.05   $17.00  
  Purchase #6 $237.70   10.859%   $263.5118   $263.51   $263.50   $263.50  
  Purchase #7 $85.40   5.738%   $90.3003   $90.30   $90.30   $90.30  
  7 purchase totals = $856.83       $935.7425   $935.74   $935.75   $935.70