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 $54.61   7.332%   $58.614   $58.61   $58.60   $58.60  
  Purchase #2 $23.60   11.212%   $26.246   $26.25   $26.25   $26.20  
  Purchase #3 $134.62   13.611%   $152.9431   $152.94   $152.95   $152.90  
  Purchase #4 $197.27   6.213%   $209.5264   $209.53   $209.55   $209.50  
  Purchase #5 $126.44   9.373%   $138.2912   $138.29   $138.30   $138.30  
  Purchase #6 $53.49   6.624%   $57.0332   $57.03   $57.05   $57.00  
  Purchase #7 $32.46   8.437%   $35.1987   $35.20   $35.20   $35.20  
  7 purchase totals = $622.49       $677.8526   $677.85   $677.90   $677.70