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	$140.83	13.553%	$159.9167	$159.92	$159.90	$159.90
Purchase #2	$69.59	12.598%	$78.3569	$78.36	$78.35	$78.40
Purchase #3	$193.54	11.238%	$215.29	$215.29	$215.30	$215.30
Purchase #4	$133.56	3.262%	$137.9167	$137.92	$137.90	$137.90
Purchase #5	$140.80	8.355%	$152.5638	$152.56	$152.55	$152.60
Purchase #6	$151.66	12.374%	$170.4264	$170.43	$170.45	$170.40
Purchase #7	$157.47	13.624%	$178.9237	$178.92	$178.90	$178.90
7 purchase totals =	$987.45		$1,093.3942	$1,093.40	$1,093.35	$1,093.40