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 $80.72   4.357%   $84.237   $84.24   $84.25   $84.20  
  Purchase #2 $169.89   7.258%   $182.2206   $182.22   $182.20   $182.20  
  Purchase #3 $80.85   4.788%   $84.7211   $84.72   $84.70   $84.70  
  Purchase #4 $180.68   8.804%   $196.5871   $196.59   $196.60   $196.60  
  Purchase #5 $44.30   4.718%   $46.3901   $46.39   $46.40   $46.40  
  Purchase #6 $187.31   8.660%   $203.531   $203.53   $203.55   $203.50  
  Purchase #7 $149.47   11.693%   $166.9475   $166.95   $166.95   $166.90  
  7 purchase totals = $893.22       $964.6344   $964.64   $964.65   $964.50