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	$51.49	10.853%	$57.0782	$57.08	$57.10	$57.10
Purchase #2	$185.93	4.639%	$194.5553	$194.56	$194.55	$194.60
Purchase #3	$33.72	4.665%	$35.293	$35.29	$35.30	$35.30
Purchase #4	$30.58	3.208%	$31.561	$31.56	$31.55	$31.60
Purchase #5	$234.42	10.630%	$259.3388	$259.34	$259.35	$259.30
Purchase #6	$159.27	5.550%	$168.1095	$168.11	$168.10	$168.10
Purchase #7	$148.91	3.531%	$154.168	$154.17	$154.15	$154.20
7 purchase totals =	$844.32		$900.1038	$900.11	$900.10	$900.20