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 $68.44   6.402%   $72.8215   $72.82   $72.80   $72.80  
  Purchase #2 $180.88   4.768%   $189.5044   $189.50   $189.50   $189.50  
  Purchase #3 $65.30   5.735%   $69.045   $69.05   $69.05   $69.00  
  Purchase #4 $177.78   10.364%   $196.2051   $196.21   $196.20   $196.20  
  Purchase #5 $96.95   4.820%   $101.623   $101.62   $101.60   $101.60  
  Purchase #6 $182.93   8.430%   $198.351   $198.35   $198.35   $198.40  
  Purchase #7 $36.30   4.601%   $37.9702   $37.97   $37.95   $38.00  
  7 purchase totals = $808.58       $865.5202   $865.52   $865.45   $865.50