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	$149.84	12.741%	$168.9311	$168.93	$168.95	$168.90
Purchase #2	$106.93	11.395%	$119.1147	$119.11	$119.10	$119.10
Purchase #3	$55.46	12.467%	$62.3742	$62.37	$62.35	$62.40
Purchase #4	$60.51	8.423%	$65.6068	$65.61	$65.60	$65.60
Purchase #5	$240.72	13.567%	$273.3785	$273.38	$273.40	$273.40
Purchase #6	$89.85	10.545%	$99.3247	$99.32	$99.30	$99.30
Purchase #7	$46.87	12.264%	$52.6181	$52.62	$52.60	$52.60
7 purchase totals =	$750.18		$841.3481	$841.34	$841.30	$841.30