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	$120.83	8.640%	$131.2697	$131.27	$131.25	$131.30
Purchase #2	$229.82	12.152%	$257.7477	$257.75	$257.75	$257.70
Purchase #3	$213.33	11.250%	$237.3296	$237.33	$237.35	$237.30
Purchase #4	$47.43	6.261%	$50.3996	$50.40	$50.40	$50.40
Purchase #5	$124.29	6.160%	$131.9463	$131.95	$131.95	$131.90
Purchase #6	$65.94	8.869%	$71.7882	$71.79	$71.80	$71.80
Purchase #7	$31.41	3.711%	$32.5756	$32.58	$32.60	$32.60
7 purchase totals =	$833.05		$913.0567	$913.07	$913.10	$913.00