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 $144.58   10.677%   $160.0168   $160.02   $160.00   $160.00  
  Purchase #2 $166.42   9.362%   $182.0002   $182.00   $182.00   $182.00  
  Purchase #3 $175.43   8.303%   $189.996   $190.00   $190.00   $190.00  
  Purchase #4 $121.99   13.405%   $138.3428   $138.34   $138.35   $138.30  
  Purchase #5 $58.80   7.660%   $63.3041   $63.30   $63.30   $63.30  
  Purchase #6 $198.64   7.501%   $213.54   $213.54   $213.55   $213.50  
  Purchase #7 $96.41   11.287%   $107.2918   $107.29   $107.30   $107.30  
  7 purchase totals = $962.27       $1,054.4917   $1,054.49   $1,054.50   $1,054.40