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 $134.62   13.277%   $152.4935   $152.49   $152.50   $152.50  
  Purchase #2 $203.95   5.147%   $214.4473   $214.45   $214.45   $214.40  
  Purchase #3 $113.91   7.810%   $122.8064   $122.81   $122.80   $122.80  
  Purchase #4 $59.80   5.811%   $63.275   $63.28   $63.30   $63.30  
  Purchase #5 $189.28   11.815%   $211.6434   $211.64   $211.65   $211.60  
  Purchase #6 $209.63   10.419%   $231.4713   $231.47   $231.45   $231.50  
  Purchase #7 $169.69   8.153%   $183.5248   $183.52   $183.50   $183.50  
  7 purchase totals = $1,080.88       $1,179.6617   $1,179.66   $1,179.65   $1,179.60