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	$42.34	4.416%	$44.2097	$44.21	$44.20	$44.20
Purchase #2	$222.72	12.144%	$249.7671	$249.77	$249.75	$249.80
Purchase #3	$197.42	6.266%	$209.7903	$209.79	$209.80	$209.80
Purchase #4	$91.54	8.210%	$99.0554	$99.06	$99.05	$99.10
Purchase #5	$131.41	9.817%	$144.3105	$144.31	$144.30	$144.30
Purchase #6	$80.40	13.178%	$90.9951	$91.00	$91.00	$91.00
Purchase #7	$217.34	8.272%	$235.3184	$235.32	$235.30	$235.30
7 purchase totals =	$983.17		$1,073.4465	$1,073.46	$1,073.40	$1,073.50