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 $54.59   7.233%   $58.5385   $58.54   $58.55   $58.50  
  Purchase #2 $130.77   4.421%   $136.5513   $136.55   $136.55   $136.60  
  Purchase #3 $161.74   12.181%   $181.4415   $181.44   $181.45   $181.40  
  Purchase #4 $47.26   13.108%   $53.4548   $53.45   $53.45   $53.50  
  Purchase #5 $72.25   11.615%   $80.6418   $80.64   $80.65   $80.60  
  Purchase #6 $88.29   8.174%   $95.5068   $95.51   $95.50   $95.50  
  Purchase #7 $81.63   6.845%   $87.2176   $87.22   $87.20   $87.20  
  7 purchase totals = $636.53       $693.3523   $693.35   $693.35   $693.30