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 $58.51   4.274%   $61.0107   $61.01   $61.00   $61.00  
  Purchase #2 $16.60   12.697%   $18.7077   $18.71   $18.70   $18.70  
  Purchase #3 $178.87   12.134%   $200.5741   $200.57   $200.55   $200.60  
  Purchase #4 $201.77   4.257%   $210.3593   $210.36   $210.35   $210.40  
  Purchase #5 $178.70   6.653%   $190.5889   $190.59   $190.60   $190.60  
  Purchase #6 $114.90   4.176%   $119.6982   $119.70   $119.70   $119.70  
  Purchase #7 $249.73   7.692%   $268.9392   $268.94   $268.95   $268.90  
  7 purchase totals = $999.08       $1,069.8781   $1,069.88   $1,069.85   $1,069.90