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	$238.34	7.755%	$256.8233	$256.82	$256.80	$256.80
Purchase #2	$51.88	12.594%	$58.4138	$58.41	$58.40	$58.40
Purchase #3	$137.95	7.352%	$148.0921	$148.09	$148.10	$148.10
Purchase #4	$162.35	3.808%	$168.5323	$168.53	$168.55	$168.50
Purchase #5	$56.72	10.218%	$62.5156	$62.52	$62.50	$62.50
Purchase #6	$143.84	4.219%	$149.9086	$149.91	$149.90	$149.90
Purchase #7	$96.72	6.742%	$103.2409	$103.24	$103.25	$103.20
7 purchase totals =	$887.80		$947.5266	$947.52	$947.50	$947.40