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 $65.46   13.118%   $74.047   $74.05   $74.05   $74.00  
  Purchase #2 $38.62   6.697%   $41.2064   $41.21   $41.20   $41.20  
  Purchase #3 $62.52   13.138%   $70.7339   $70.73   $70.75   $70.70  
  Purchase #4 $126.27   4.350%   $131.7627   $131.76   $131.75   $131.80  
  Purchase #5 $175.72   5.592%   $185.5463   $185.55   $185.55   $185.50  
  Purchase #6 $87.60   8.739%   $95.2554   $95.26   $95.25   $95.30  
  Purchase #7 $14.59   3.446%   $15.0928   $15.09   $15.10   $15.10  
  7 purchase totals = $570.78       $613.6445   $613.65   $613.65   $613.60