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	$141.90	12.175%	$159.1763	$159.18	$159.20	$159.20
Purchase #2	$73.94	5.564%	$78.054	$78.05	$78.05	$78.10
Purchase #3	$71.61	12.523%	$80.5777	$80.58	$80.60	$80.60
Purchase #4	$55.39	7.856%	$59.7414	$59.74	$59.75	$59.70
Purchase #5	$175.64	13.855%	$199.9749	$199.97	$199.95	$200.00
Purchase #6	$215.94	12.192%	$242.2674	$242.27	$242.25	$242.30
Purchase #7	$76.33	5.617%	$80.6175	$80.62	$80.60	$80.60
7 purchase totals =	$810.75		$900.4092	$900.41	$900.40	$900.50