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	$16.46	9.650%	$18.0484	$18.05	$18.05	$18.00
Purchase #2	$32.57	5.219%	$34.2698	$34.27	$34.25	$34.30
Purchase #3	$79.81	3.214%	$82.3751	$82.38	$82.40	$82.40
Purchase #4	$147.44	9.515%	$161.4689	$161.47	$161.45	$161.50
Purchase #5	$48.75	3.126%	$50.2739	$50.27	$50.25	$50.30
Purchase #6	$50.51	5.750%	$53.4143	$53.41	$53.40	$53.40
Purchase #7	$59.79	5.165%	$62.8782	$62.88	$62.90	$62.90
7 purchase totals =	$435.33		$462.7286	$462.73	$462.70	$462.80