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	$47.92	11.269%	$53.3201	$53.32	$53.30	$53.30
Purchase #2	$77.35	7.131%	$82.8658	$82.87	$82.85	$82.90
Purchase #3	$90.53	8.373%	$98.1101	$98.11	$98.10	$98.10
Purchase #4	$80.58	13.524%	$91.4776	$91.48	$91.50	$91.50
Purchase #5	$163.36	13.321%	$185.1212	$185.12	$185.10	$185.10
Purchase #6	$63.98	12.331%	$71.8694	$71.87	$71.85	$71.90
Purchase #7	$203.80	9.320%	$222.7942	$222.79	$222.80	$222.80
7 purchase totals =	$727.52		$805.5584	$805.56	$805.50	$805.60