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 $61.62   8.626%   $66.9353   $66.94   $66.95   $66.90  
  Purchase #2 $226.88   6.225%   $241.0033   $241.00   $241.00   $241.00  
  Purchase #3 $111.62   5.203%   $117.4276   $117.43   $117.45   $117.40  
  Purchase #4 $22.79   10.294%   $25.136   $25.14   $25.15   $25.10  
  Purchase #5 $104.72   12.176%   $117.4707   $117.47   $117.45   $117.50  
  Purchase #6 $228.82   13.665%   $260.0883   $260.09   $260.10   $260.10  
  Purchase #7 $92.32   12.346%   $103.7178   $103.72   $103.70   $103.70  
  7 purchase totals = $848.77       $931.7790   $931.79   $931.80   $931.70