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 $64.53   13.222%   $73.0622   $73.06   $73.05   $73.10  
  Purchase #2 $226.75   5.857%   $240.0307   $240.03   $240.05   $240.00  
  Purchase #3 $55.47   10.677%   $61.3925   $61.39   $61.40   $61.40  
  Purchase #4 $108.62   13.834%   $123.6465   $123.65   $123.65   $123.60  
  Purchase #5 $50.47   3.628%   $52.3011   $52.30   $52.30   $52.30  
  Purchase #6 $84.33   8.754%   $91.7122   $91.71   $91.70   $91.70  
  Purchase #7 $152.73   5.313%   $160.8445   $160.84   $160.85   $160.80  
  7 purchase totals = $742.90       $802.9897   $802.98   $803.00   $802.90