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	$37.46	9.479%	$41.0108	$41.01	$41.00	$41.00
Purchase #2	$196.45	8.113%	$212.388	$212.39	$212.40	$212.40
Purchase #3	$77.95	6.379%	$82.9224	$82.92	$82.90	$82.90
Purchase #4	$147.50	8.233%	$159.6437	$159.64	$159.65	$159.60
Purchase #5	$82.76	3.170%	$85.3835	$85.38	$85.40	$85.40
Purchase #6	$126.97	11.695%	$141.8191	$141.82	$141.80	$141.80
Purchase #7	$115.50	12.122%	$129.5009	$129.50	$129.50	$129.50
7 purchase totals =	$784.59		$852.6684	$852.66	$852.65	$852.60