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 $53.38   8.550%   $57.944   $57.94   $57.95   $57.90  
  Purchase #2 $96.35   3.357%   $99.5845   $99.58   $99.60   $99.60  
  Purchase #3 $155.32   7.102%   $166.3508   $166.35   $166.35   $166.40  
  Purchase #4 $232.72   12.737%   $262.3615   $262.36   $262.35   $262.40  
  Purchase #5 $238.58   11.387%   $265.7471   $265.75   $265.75   $265.70  
  Purchase #6 $150.62   6.786%   $160.8411   $160.84   $160.85   $160.80  
  Purchase #7 $72.61   5.410%   $76.5382   $76.54   $76.55   $76.50  
  7 purchase totals = $999.58       $1,089.3672   $1,089.36   $1,089.40   $1,089.30