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	$159.39	5.257%	$167.7691	$167.77	$167.75	$167.80
Purchase #2	$213.94	12.584%	$240.8622	$240.86	$240.85	$240.90
Purchase #3	$144.51	10.462%	$159.6286	$159.63	$159.65	$159.60
Purchase #4	$248.61	10.640%	$275.0621	$275.06	$275.05	$275.10
Purchase #5	$144.94	13.663%	$164.7432	$164.74	$164.75	$164.70
Purchase #6	$212.65	5.280%	$223.8779	$223.88	$223.90	$223.90
Purchase #7	$64.91	9.591%	$71.1355	$71.14	$71.15	$71.10
7 purchase totals =	$1,188.95		$1,303.0786	$1,303.08	$1,303.10	$1,303.10