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 $61.45   7.369%   $65.9783   $65.98   $66.00   $66.00  
  Purchase #2 $234.51   13.521%   $266.2181   $266.22   $266.20   $266.20  
  Purchase #3 $87.90   5.855%   $93.0465   $93.05   $93.05   $93.00  
  Purchase #4 $185.54   7.844%   $200.0938   $200.09   $200.10   $200.10  
  Purchase #5 $237.36   11.608%   $264.9127   $264.91   $264.90   $264.90  
  Purchase #6 $17.85   12.627%   $20.1039   $20.10   $20.10   $20.10  
  Purchase #7 $90.44   6.676%   $96.4778   $96.48   $96.50   $96.50  
  7 purchase totals = $915.05       $1,006.8311   $1,006.83   $1,006.85   $1,006.80