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 $92.57   5.641%   $97.7919   $97.79   $97.80   $97.80  
  Purchase #2 $136.69   13.350%   $154.9381   $154.94   $154.95   $154.90  
  Purchase #3 $57.35   6.340%   $60.986   $60.99   $61.00   $61.00  
  Purchase #4 $242.85   6.866%   $259.5241   $259.52   $259.50   $259.50  
  Purchase #5 $35.89   6.198%   $38.1145   $38.11   $38.10   $38.10  
  Purchase #6 $210.62   11.382%   $234.5928   $234.59   $234.60   $234.60  
  Purchase #7 $215.32   4.824%   $225.707   $225.71   $225.70   $225.70  
  7 purchase totals = $991.29       $1,071.6544   $1,071.65   $1,071.65   $1,071.60