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	$32.79	5.163%	$34.4829	$34.48	$34.50	$34.50
Purchase #2	$221.83	9.220%	$242.2827	$242.28	$242.30	$242.30
Purchase #3	$104.51	5.213%	$109.9581	$109.96	$109.95	$110.00
Purchase #4	$18.53	10.526%	$20.4805	$20.48	$20.50	$20.50
Purchase #5	$75.32	9.749%	$82.6629	$82.66	$82.65	$82.70
Purchase #6	$233.30	11.244%	$259.5323	$259.53	$259.55	$259.50
Purchase #7	$43.98	3.318%	$45.4393	$45.44	$45.45	$45.40
7 purchase totals =	$730.26		$794.8387	$794.83	$794.90	$794.90