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	$79.33	13.214%	$89.8127	$89.81	$89.80	$89.80
Purchase #2	$131.69	3.435%	$136.2136	$136.21	$136.20	$136.20
Purchase #3	$75.82	13.162%	$85.7994	$85.80	$85.80	$85.80
Purchase #4	$182.62	5.598%	$192.8431	$192.84	$192.85	$192.80
Purchase #5	$186.64	7.798%	$201.1942	$201.19	$201.20	$201.20
Purchase #6	$216.27	12.320%	$242.9145	$242.91	$242.90	$242.90
Purchase #7	$79.75	12.140%	$89.4317	$89.43	$89.45	$89.40
7 purchase totals =	$952.12		$1,038.2092	$1,038.19	$1,038.20	$1,038.10