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	$241.76	10.809%	$267.8918	$267.89	$267.90	$267.90
Purchase #2	$112.46	13.196%	$127.3002	$127.30	$127.30	$127.30
Purchase #3	$42.69	9.745%	$46.8501	$46.85	$46.85	$46.90
Purchase #4	$154.73	12.831%	$174.5834	$174.58	$174.60	$174.60
Purchase #5	$168.42	9.348%	$184.1639	$184.16	$184.15	$184.20
Purchase #6	$110.48	7.870%	$119.1748	$119.17	$119.15	$119.20
Purchase #7	$178.98	5.123%	$188.1491	$188.15	$188.15	$188.10
7 purchase totals =	$1,009.52		$1,108.1133	$1,108.10	$1,108.10	$1,108.20