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 $165.79   8.723%   $180.2519   $180.25   $180.25   $180.30  
  Purchase #2 $200.64   13.363%   $227.4515   $227.45   $227.45   $227.50  
  Purchase #3 $118.39   5.232%   $124.5842   $124.58   $124.60   $124.60  
  Purchase #4 $84.58   8.714%   $91.9503   $91.95   $91.95   $92.00  
  Purchase #5 $245.70   5.422%   $259.0219   $259.02   $259.00   $259.00  
  Purchase #6 $30.91   8.268%   $33.4656   $33.47   $33.45   $33.50  
  Purchase #7 $89.44   8.441%   $96.9896   $96.99   $97.00   $97.00  
  7 purchase totals = $935.45       $1,013.7150   $1,013.71   $1,013.70   $1,013.90