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 $95.66   7.249%   $102.5944   $102.59   $102.60   $102.60  
  Purchase #2 $43.94   8.407%   $47.634   $47.63   $47.65   $47.60  
  Purchase #3 $49.95   7.323%   $53.6078   $53.61   $53.60   $53.60  
  Purchase #4 $70.53   8.781%   $76.7232   $76.72   $76.70   $76.70  
  Purchase #5 $241.39   10.621%   $267.028   $267.03   $267.05   $267.00  
  Purchase #6 $14.94   13.831%   $17.0064   $17.01   $17.00   $17.00  
  Purchase #7 $210.86   9.778%   $231.4779   $231.48   $231.50   $231.50  
  7 purchase totals = $727.27       $796.0717   $796.07   $796.10   $796.00