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 $59.67   3.586%   $61.8098   $61.81   $61.80   $61.80  
  Purchase #2 $199.42   13.635%   $226.6109   $226.61   $226.60   $226.60  
  Purchase #3 $127.65   10.470%   $141.015   $141.02   $141.00   $141.00  
  Purchase #4 $116.31   5.723%   $122.9664   $122.97   $122.95   $123.00  
  Purchase #5 $218.46   3.746%   $226.6435   $226.64   $226.65   $226.60  
  Purchase #6 $108.62   5.620%   $114.7244   $114.72   $114.70   $114.70  
  Purchase #7 $162.84   5.544%   $171.8678   $171.87   $171.85   $171.90  
  7 purchase totals = $992.97       $1,065.6378   $1,065.64   $1,065.55   $1,065.60