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 $68.27   12.179%   $76.5846   $76.58   $76.60   $76.60  
  Purchase #2 $88.71   13.422%   $100.6167   $100.62   $100.60   $100.60  
  Purchase #3 $220.39   7.662%   $237.2763   $237.28   $237.30   $237.30  
  Purchase #4 $122.42   11.869%   $136.95   $136.95   $136.95   $137.00  
  Purchase #5 $38.83   11.244%   $43.196   $43.20   $43.20   $43.20  
  Purchase #6 $48.70   12.478%   $54.7768   $54.78   $54.80   $54.80  
  Purchase #7 $81.62   7.104%   $87.4183   $87.42   $87.40   $87.40  
  7 purchase totals = $668.94       $736.8187   $736.83   $736.85   $736.90