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	$232.41	13.385%	$263.5181	$263.52	$263.50	$263.50
Purchase #2	$157.83	6.389%	$167.9138	$167.91	$167.90	$167.90
Purchase #3	$250.36	10.374%	$276.3323	$276.33	$276.35	$276.30
Purchase #4	$90.26	10.116%	$99.3907	$99.39	$99.40	$99.40
Purchase #5	$79.62	4.263%	$83.0142	$83.01	$83.00	$83.00
Purchase #6	$81.67	9.154%	$89.1461	$89.15	$89.15	$89.10
Purchase #7	$90.88	13.476%	$103.127	$103.13	$103.15	$103.10
7 purchase totals =	$983.03		$1,082.4422	$1,082.44	$1,082.45	$1,082.30