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	$220.61	8.226%	$238.7574	$238.76	$238.75	$238.80
Purchase #2	$30.58	9.133%	$33.3729	$33.37	$33.35	$33.40
Purchase #3	$93.59	8.324%	$101.3804	$101.38	$101.40	$101.40
Purchase #4	$128.89	11.794%	$144.0913	$144.09	$144.10	$144.10
Purchase #5	$182.54	4.170%	$190.1519	$190.15	$190.15	$190.20
Purchase #6	$55.33	6.412%	$58.8778	$58.88	$58.90	$58.90
Purchase #7	$78.72	9.435%	$86.1472	$86.15	$86.15	$86.10
7 purchase totals =	$790.26		$852.7789	$852.78	$852.80	$852.90