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	$126.63	7.482%	$136.1045	$136.10	$136.10	$136.10
Purchase #2	$35.78	8.423%	$38.7937	$38.79	$38.80	$38.80
Purchase #3	$65.37	9.661%	$71.6854	$71.69	$71.70	$71.70
Purchase #4	$6.82	6.675%	$7.2752	$7.28	$7.30	$7.30
Purchase #5	$78.95	4.215%	$82.2777	$82.28	$82.30	$82.30
Purchase #6	$223.41	6.264%	$237.4044	$237.40	$237.40	$237.40
Purchase #7	$36.39	3.496%	$37.6622	$37.66	$37.65	$37.70
7 purchase totals =	$573.35		$611.2031	$611.20	$611.25	$611.30