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	$165.65	13.106%	$187.3601	$187.36	$187.35	$187.40
Purchase #2	$149.55	7.666%	$161.0145	$161.01	$161.00	$161.00
Purchase #3	$99.82	9.799%	$109.6014	$109.60	$109.60	$109.60
Purchase #4	$145.78	6.294%	$154.9554	$154.96	$154.95	$155.00
Purchase #5	$141.25	12.672%	$159.1492	$159.15	$159.15	$159.10
Purchase #6	$250.36	9.659%	$274.5423	$274.54	$274.55	$274.50
Purchase #7	$29.37	9.868%	$32.2682	$32.27	$32.25	$32.30
7 purchase totals =	$981.78		$1,078.8911	$1,078.89	$1,078.85	$1,078.90