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	$28.53	3.336%	$29.4818	$29.48	$29.50	$29.50
Purchase #2	$180.89	4.234%	$188.5489	$188.55	$188.55	$188.50
Purchase #3	$11.85	13.713%	$13.475	$13.48	$13.50	$13.50
Purchase #4	$156.82	12.114%	$175.8172	$175.82	$175.80	$175.80
Purchase #5	$72.74	4.792%	$76.2257	$76.23	$76.25	$76.20
Purchase #6	$102.64	13.317%	$116.3086	$116.31	$116.30	$116.30
Purchase #7	$23.75	6.752%	$25.3536	$25.35	$25.35	$25.40
7 purchase totals =	$577.22		$625.2108	$625.22	$625.25	$625.20