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	$33.50	4.239%	$34.9201	$34.92	$34.90	$34.90
Purchase #2	$27.83	13.399%	$31.5589	$31.56	$31.55	$31.60
Purchase #3	$227.97	8.375%	$247.0625	$247.06	$247.05	$247.10
Purchase #4	$40.88	3.746%	$42.4114	$42.41	$42.40	$42.40
Purchase #5	$35.96	13.624%	$40.8592	$40.86	$40.85	$40.90
Purchase #6	$60.66	3.751%	$62.9354	$62.94	$62.95	$62.90
Purchase #7	$93.59	6.815%	$99.9682	$99.97	$99.95	$100.00
7 purchase totals =	$520.39		$559.7157	$559.72	$559.65	$559.80