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	$51.89	6.402%	$55.212	$55.21	$55.20	$55.20
Purchase #2	$128.28	4.314%	$133.814	$133.81	$133.80	$133.80
Purchase #3	$94.57	5.668%	$99.9302	$99.93	$99.95	$99.90
Purchase #4	$46.42	10.280%	$51.192	$51.19	$51.20	$51.20
Purchase #5	$190.97	10.690%	$211.3847	$211.38	$211.40	$211.40
Purchase #6	$190.42	5.428%	$200.756	$200.76	$200.75	$200.80
Purchase #7	$94.40	5.706%	$99.7865	$99.79	$99.80	$99.80
7 purchase totals =	$796.95		$852.0754	$852.07	$852.10	$852.10