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	$55.60	6.592%	$59.2652	$59.27	$59.25	$59.30
Purchase #2	$56.74	7.223%	$60.8383	$60.84	$60.85	$60.80
Purchase #3	$100.58	9.275%	$109.9088	$109.91	$109.90	$109.90
Purchase #4	$7.50	11.496%	$8.3622	$8.36	$8.35	$8.40
Purchase #5	$202.33	12.718%	$228.0623	$228.06	$228.05	$228.10
Purchase #6	$93.85	12.791%	$105.8544	$105.85	$105.85	$105.90
Purchase #7	$192.36	12.255%	$215.9337	$215.93	$215.95	$215.90
7 purchase totals =	$708.96		$788.2249	$788.22	$788.20	$788.30