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 $180.62   3.131%   $186.2752   $186.28   $186.30   $186.30  
  Purchase #2 $104.54   11.245%   $116.2955   $116.30   $116.30   $116.30  
  Purchase #3 $221.80   6.196%   $235.5427   $235.54   $235.55   $235.50  
  Purchase #4 $163.66   8.470%   $177.522   $177.52   $177.50   $177.50  
  Purchase #5 $53.65   10.414%   $59.2371   $59.24   $59.25   $59.20  
  Purchase #6 $15.69   9.688%   $17.21   $17.21   $17.20   $17.20  
  Purchase #7 $205.46   8.329%   $222.5728   $222.57   $222.55   $222.60  
  7 purchase totals = $945.42       $1,014.6553   $1,014.66   $1,014.65   $1,014.60