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	$91.39	8.669%	$99.3126	$99.31	$99.30	$99.30
Purchase #2	$195.34	13.429%	$221.5722	$221.57	$221.55	$221.60
Purchase #3	$33.31	13.729%	$37.8831	$37.88	$37.90	$37.90
Purchase #4	$182.80	13.471%	$207.425	$207.43	$207.45	$207.40
Purchase #5	$129.34	7.846%	$139.488	$139.49	$139.50	$139.50
Purchase #6	$225.29	6.531%	$240.0037	$240.00	$240.00	$240.00
Purchase #7	$133.39	11.481%	$148.7045	$148.70	$148.70	$148.70
7 purchase totals =	$990.86		$1,094.3891	$1,094.38	$1,094.40	$1,094.40