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 $38.41   13.650%   $43.653   $43.65   $43.65   $43.70  
  Purchase #2 $66.64   3.242%   $68.8005   $68.80   $68.80   $68.80  
  Purchase #3 $60.45   8.387%   $65.5199   $65.52   $65.50   $65.50  
  Purchase #4 $116.61   5.173%   $122.6422   $122.64   $122.65   $122.60  
  Purchase #5 $102.25   13.521%   $116.0752   $116.08   $116.10   $116.10  
  Purchase #6 $209.57   7.333%   $224.9378   $224.94   $224.95   $224.90  
  Purchase #7 $196.74   10.795%   $217.9781   $217.98   $218.00   $218.00  
  7 purchase totals = $790.67       $859.6067   $859.61   $859.65   $859.60