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	$43.79	3.861%	$45.4807	$45.48	$45.50	$45.50
Purchase #2	$214.46	12.681%	$241.6557	$241.66	$241.65	$241.70
Purchase #3	$178.86	3.742%	$185.5529	$185.55	$185.55	$185.60
Purchase #4	$158.30	8.280%	$171.4072	$171.41	$171.40	$171.40
Purchase #5	$190.40	11.384%	$212.0751	$212.08	$212.10	$212.10
Purchase #6	$144.94	10.223%	$159.7572	$159.76	$159.75	$159.80
Purchase #7	$213.78	11.753%	$238.9056	$238.91	$238.90	$238.90
7 purchase totals =	$1,144.53		$1,254.8344	$1,254.85	$1,254.85	$1,255.00