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	$115.75	13.445%	$131.3126	$131.31	$131.30	$131.30
Purchase #2	$248.54	9.837%	$272.9889	$272.99	$273.00	$273.00
Purchase #3	$221.33	4.293%	$230.8317	$230.83	$230.85	$230.80
Purchase #4	$154.85	10.447%	$171.0272	$171.03	$171.05	$171.00
Purchase #5	$88.64	11.800%	$99.0995	$99.10	$99.10	$99.10
Purchase #6	$88.35	12.505%	$99.3982	$99.40	$99.40	$99.40
Purchase #7	$133.59	7.135%	$143.1216	$143.12	$143.10	$143.10
7 purchase totals =	$1,051.05		$1,147.7797	$1,147.78	$1,147.80	$1,147.70