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	$229.71	3.764%	$238.3563	$238.36	$238.35	$238.40
Purchase #2	$172.29	10.187%	$189.8412	$189.84	$189.85	$189.80
Purchase #3	$168.29	8.289%	$182.2396	$182.24	$182.25	$182.20
Purchase #4	$12.91	3.203%	$13.3235	$13.32	$13.30	$13.30
Purchase #5	$222.72	13.838%	$253.54	$253.54	$253.55	$253.50
Purchase #6	$49.59	13.668%	$56.368	$56.37	$56.35	$56.40
Purchase #7	$64.81	8.816%	$70.5236	$70.52	$70.50	$70.50
7 purchase totals =	$920.32		$1,004.1922	$1,004.19	$1,004.15	$1,004.10