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	$137.93	13.402%	$156.4154	$156.42	$156.40	$156.40
Purchase #2	$97.90	5.486%	$103.2708	$103.27	$103.25	$103.30
Purchase #3	$248.84	6.407%	$264.7832	$264.78	$264.80	$264.80
Purchase #4	$212.41	5.181%	$223.415	$223.42	$223.40	$223.40
Purchase #5	$231.73	13.776%	$263.6531	$263.65	$263.65	$263.70
Purchase #6	$235.53	6.487%	$250.8088	$250.81	$250.80	$250.80
Purchase #7	$40.52	5.309%	$42.6712	$42.67	$42.65	$42.70
7 purchase totals =	$1,204.86		$1,305.0175	$1,305.02	$1,304.95	$1,305.10