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	$135.46	9.655%	$148.5387	$148.54	$148.55	$148.50
Purchase #2	$189.39	6.361%	$201.4371	$201.44	$201.45	$201.40
Purchase #3	$66.40	5.228%	$69.8714	$69.87	$69.85	$69.90
Purchase #4	$98.84	12.514%	$111.2088	$111.21	$111.20	$111.20
Purchase #5	$106.48	5.696%	$112.5451	$112.55	$112.55	$112.50
Purchase #6	$47.52	13.445%	$53.9091	$53.91	$53.90	$53.90
Purchase #7	$101.42	9.534%	$111.0894	$111.09	$111.10	$111.10
7 purchase totals =	$745.51		$808.5996	$808.61	$808.60	$808.50