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 $160.47   13.509%   $182.1479   $182.15   $182.15   $182.10  
  Purchase #2 $150.81   10.185%   $166.17   $166.17   $166.15   $166.20  
  Purchase #3 $20.25   11.170%   $22.5119   $22.51   $22.50   $22.50  
  Purchase #4 $95.75   13.385%   $108.5661   $108.57   $108.55   $108.60  
  Purchase #5 $204.46   8.844%   $222.5424   $222.54   $222.55   $222.50  
  Purchase #6 $156.63   4.637%   $163.8929   $163.89   $163.90   $163.90  
  Purchase #7 $158.88   7.421%   $170.6705   $170.67   $170.65   $170.70  
  7 purchase totals = $947.25       $1,036.5017   $1,036.50   $1,036.45   $1,036.50