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	$172.28	9.631%	$188.8723	$188.87	$188.85	$188.90
Purchase #2	$73.94	6.690%	$78.8866	$78.89	$78.90	$78.90
Purchase #3	$72.53	13.202%	$82.1054	$82.11	$82.10	$82.10
Purchase #4	$107.92	9.157%	$117.8022	$117.80	$117.80	$117.80
Purchase #5	$86.42	13.618%	$98.1887	$98.19	$98.20	$98.20
Purchase #6	$229.78	13.602%	$261.0347	$261.03	$261.05	$261.00
Purchase #7	$242.39	11.649%	$270.626	$270.63	$270.65	$270.60
7 purchase totals =	$985.26		$1,097.5159	$1,097.52	$1,097.55	$1,097.50