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 $87.70   9.436%   $95.9754   $95.98   $96.00   $96.00  
  Purchase #2 $200.72   13.443%   $227.7028   $227.70   $227.70   $227.70  
  Purchase #3 $61.52   5.496%   $64.9011   $64.90   $64.90   $64.90  
  Purchase #4 $24.98   10.393%   $27.5762   $27.58   $27.60   $27.60  
  Purchase #5 $234.53   5.811%   $248.1585   $248.16   $248.15   $248.20  
  Purchase #6 $73.47   5.173%   $77.2706   $77.27   $77.25   $77.30  
  Purchase #7 $248.62   6.626%   $265.0936   $265.09   $265.10   $265.10  
  7 purchase totals = $931.54       $1,006.6782   $1,006.68   $1,006.70   $1,006.80