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 $68.63   12.236%   $77.0276   $77.03   $77.05   $77.00  
  Purchase #2 $25.91   8.381%   $28.0815   $28.08   $28.10   $28.10  
  Purchase #3 $54.26   7.429%   $58.291   $58.29   $58.30   $58.30  
  Purchase #4 $65.87   6.564%   $70.1937   $70.19   $70.20   $70.20  
  Purchase #5 $200.78   7.346%   $215.5293   $215.53   $215.55   $215.50  
  Purchase #6 $55.53   5.292%   $58.4686   $58.47   $58.45   $58.50  
  Purchase #7 $47.84   13.213%   $54.1611   $54.16   $54.15   $54.20  
  7 purchase totals = $518.82       $561.7528   $561.75   $561.80   $561.80