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 $53.97   13.731%   $61.3806   $61.38   $61.40   $61.40  
  Purchase #2 $241.94   7.574%   $260.2645   $260.26   $260.25   $260.30  
  Purchase #3 $57.53   5.455%   $60.6683   $60.67   $60.65   $60.70  
  Purchase #4 $247.90   8.527%   $269.0384   $269.04   $269.05   $269.00  
  Purchase #5 $103.70   12.197%   $116.3483   $116.35   $116.35   $116.30  
  Purchase #6 $159.86   8.553%   $173.5328   $173.53   $173.55   $173.50  
  Purchase #7 $122.37   5.843%   $129.5201   $129.52   $129.50   $129.50  
  7 purchase totals = $987.27       $1,070.7530   $1,070.75   $1,070.75   $1,070.70