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 $165.66   6.451%   $176.3467   $176.35   $176.35   $176.30  
  Purchase #2 $25.63   6.520%   $27.3011   $27.30   $27.30   $27.30  
  Purchase #3 $16.50   6.177%   $17.5192   $17.52   $17.50   $17.50  
  Purchase #4 $211.36   5.255%   $222.467   $222.47   $222.45   $222.50  
  Purchase #5 $191.36   8.280%   $207.2046   $207.20   $207.20   $207.20  
  Purchase #6 $240.48   4.769%   $251.9485   $251.95   $251.95   $251.90  
  Purchase #7 $93.83   8.347%   $101.662   $101.66   $101.65   $101.70  
  7 purchase totals = $944.82       $1,004.4491   $1,004.45   $1,004.40   $1,004.40