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 $52.56   7.600%   $56.5546   $56.55   $56.55   $56.60  
  Purchase #2 $84.59   13.599%   $96.0934   $96.09   $96.10   $96.10  
  Purchase #3 $32.26   3.787%   $33.4817   $33.48   $33.50   $33.50  
  Purchase #4 $53.32   13.229%   $60.3737   $60.37   $60.35   $60.40  
  Purchase #5 $180.96   13.836%   $205.9976   $206.00   $206.00   $206.00  
  Purchase #6 $74.63   9.680%   $81.8542   $81.85   $81.85   $81.90  
  Purchase #7 $135.25   4.642%   $141.5283   $141.53   $141.55   $141.50  
  7 purchase totals = $613.57       $675.8835   $675.87   $675.90   $676.00