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 $51.87   10.560%   $57.3475   $57.35   $57.35   $57.30  
  Purchase #2 $200.72   7.236%   $215.2441   $215.24   $215.25   $215.20  
  Purchase #3 $96.99   11.841%   $108.4746   $108.47   $108.45   $108.50  
  Purchase #4 $243.84   8.655%   $264.9444   $264.94   $264.95   $264.90  
  Purchase #5 $68.78   7.437%   $73.8952   $73.90   $73.90   $73.90  
  Purchase #6 $177.92   7.246%   $190.8121   $190.81   $190.80   $190.80  
  Purchase #7 $154.90   7.119%   $165.9273   $165.93   $165.95   $165.90  
  7 purchase totals = $995.02       $1,076.6452   $1,076.64   $1,076.65   $1,076.50