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	$246.41	13.474%	$279.6113	$279.61	$279.60	$279.60
Purchase #2	$210.86	4.665%	$220.6966	$220.70	$220.70	$220.70
Purchase #3	$79.33	11.323%	$88.3125	$88.31	$88.30	$88.30
Purchase #4	$112.66	7.297%	$120.8808	$120.88	$120.90	$120.90
Purchase #5	$71.69	10.256%	$79.0425	$79.04	$79.05	$79.00
Purchase #6	$201.48	5.675%	$212.914	$212.91	$212.90	$212.90
Purchase #7	$94.73	4.621%	$99.1075	$99.11	$99.10	$99.10
7 purchase totals =	$1,017.16		$1,100.5652	$1,100.56	$1,100.55	$1,100.50