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 $57.95   10.868%   $64.248   $64.25   $64.25   $64.20  
  Purchase #2 $77.41   7.422%   $83.1554   $83.16   $83.15   $83.20  
  Purchase #3 $53.93   12.699%   $60.7786   $60.78   $60.80   $60.80  
  Purchase #4 $133.74   7.654%   $143.9765   $143.98   $144.00   $144.00  
  Purchase #5 $27.82   5.758%   $29.4219   $29.42   $29.40   $29.40  
  Purchase #6 $121.84   5.126%   $128.0855   $128.09   $128.10   $128.10  
  Purchase #7 $182.67   13.820%   $207.915   $207.92   $207.90   $207.90  
  7 purchase totals = $655.36       $717.5809   $717.60   $717.60   $717.60