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 $50.56   9.487%   $55.3566   $55.36   $55.35   $55.40  
  Purchase #2 $72.66   5.593%   $76.7239   $76.72   $76.70   $76.70  
  Purchase #3 $98.97   5.363%   $104.2778   $104.28   $104.30   $104.30  
  Purchase #4 $55.85   10.843%   $61.9058   $61.91   $61.90   $61.90  
  Purchase #5 $193.52   7.830%   $208.6726   $208.67   $208.65   $208.70  
  Purchase #6 $197.90   4.514%   $206.8332   $206.83   $206.85   $206.80  
  Purchase #7 $44.31   4.353%   $46.2388   $46.24   $46.25   $46.20  
  7 purchase totals = $713.77       $760.0087   $760.01   $760.00   $760.00