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	$115.56	11.138%	$128.4311	$128.43	$128.45	$128.40
Purchase #2	$245.30	12.478%	$275.9085	$275.91	$275.90	$275.90
Purchase #3	$83.25	5.868%	$88.1351	$88.14	$88.15	$88.10
Purchase #4	$26.69	4.152%	$27.7982	$27.80	$27.80	$27.80
Purchase #5	$236.72	4.500%	$247.3724	$247.37	$247.35	$247.40
Purchase #6	$84.94	8.296%	$91.9866	$91.99	$92.00	$92.00
Purchase #7	$80.76	11.269%	$89.8608	$89.86	$89.85	$89.90
7 purchase totals =	$873.22		$949.4927	$949.50	$949.50	$949.50