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	$109.71	13.191%	$124.1818	$124.18	$124.20	$124.20
Purchase #2	$219.85	10.529%	$242.998	$243.00	$243.00	$243.00
Purchase #3	$31.64	9.354%	$34.5996	$34.60	$34.60	$34.60
Purchase #4	$73.60	12.287%	$82.6432	$82.64	$82.65	$82.60
Purchase #5	$231.27	7.140%	$247.7827	$247.78	$247.80	$247.80
Purchase #6	$167.95	4.102%	$174.8393	$174.84	$174.85	$174.80
Purchase #7	$184.50	10.731%	$204.2987	$204.30	$204.30	$204.30
7 purchase totals =	$1,018.52		$1,111.3433	$1,111.34	$1,111.40	$1,111.30