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	$136.82	3.404%	$141.4774	$141.48	$141.50	$141.50
Purchase #2	$210.37	8.742%	$228.7605	$228.76	$228.75	$228.80
Purchase #3	$183.98	3.111%	$189.7036	$189.70	$189.70	$189.70
Purchase #4	$85.25	6.755%	$91.0086	$91.01	$91.00	$91.00
Purchase #5	$118.88	9.706%	$130.4185	$130.42	$130.40	$130.40
Purchase #6	$188.73	4.187%	$196.6321	$196.63	$196.65	$196.60
Purchase #7	$59.35	13.662%	$67.4584	$67.46	$67.45	$67.50
7 purchase totals =	$983.38		$1,045.4591	$1,045.46	$1,045.45	$1,045.50