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	$83.38	7.719%	$89.8161	$89.82	$89.80	$89.80
Purchase #2	$42.46	8.626%	$46.1226	$46.12	$46.10	$46.10
Purchase #3	$245.74	10.621%	$271.84	$271.84	$271.85	$271.80
Purchase #4	$218.64	13.831%	$248.8801	$248.88	$248.90	$248.90
Purchase #5	$98.37	8.172%	$106.4088	$106.41	$106.40	$106.40
Purchase #6	$172.38	4.871%	$180.7766	$180.78	$180.80	$180.80
Purchase #7	$149.88	4.554%	$156.7055	$156.71	$156.70	$156.70
7 purchase totals =	$1,010.85		$1,100.5497	$1,100.56	$1,100.55	$1,100.50