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	$53.72	7.592%	$57.7984	$57.80	$57.80	$57.80
Purchase #2	$43.65	6.872%	$46.6496	$46.65	$46.65	$46.60
Purchase #3	$250.72	7.119%	$268.5688	$268.57	$268.55	$268.60
Purchase #4	$50.49	12.773%	$56.9391	$56.94	$56.95	$56.90
Purchase #5	$141.96	3.632%	$147.116	$147.12	$147.10	$147.10
Purchase #6	$21.30	10.315%	$23.4971	$23.50	$23.50	$23.50
Purchase #7	$39.88	7.607%	$42.9137	$42.91	$42.90	$42.90
7 purchase totals =	$601.72		$643.4827	$643.49	$643.45	$643.40