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 $67.52   8.627%   $73.345   $73.35   $73.35   $73.30  
  Purchase #2 $115.81   3.326%   $119.6618   $119.66   $119.65   $119.70  
  Purchase #3 $108.83   5.730%   $115.066   $115.07   $115.05   $115.10  
  Purchase #4 $62.66   13.550%   $71.1504   $71.15   $71.15   $71.20  
  Purchase #5 $204.98   9.578%   $224.613   $224.61   $224.60   $224.60  
  Purchase #6 $91.27   5.587%   $96.3693   $96.37   $96.35   $96.40  
  Purchase #7 $79.57   13.475%   $90.2921   $90.29   $90.30   $90.30  
  7 purchase totals = $730.64       $790.4976   $790.50   $790.45   $790.60