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	$28.81	7.688%	$31.0249	$31.02	$31.00	$31.00
Purchase #2	$131.41	11.203%	$146.1319	$146.13	$146.15	$146.10
Purchase #3	$64.65	6.107%	$68.5982	$68.60	$68.60	$68.60
Purchase #4	$45.59	4.780%	$47.7692	$47.77	$47.75	$47.80
Purchase #5	$40.98	11.355%	$45.6333	$45.63	$45.65	$45.60
Purchase #6	$96.41	3.459%	$99.7448	$99.74	$99.75	$99.70
Purchase #7	$17.72	12.361%	$19.9104	$19.91	$19.90	$19.90
7 purchase totals =	$425.57		$458.8127	$458.80	$458.80	$458.70