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	$87.27	4.197%	$90.9327	$90.93	$90.95	$90.90
Purchase #2	$167.95	6.174%	$178.3192	$178.32	$178.30	$178.30
Purchase #3	$228.75	6.367%	$243.3145	$243.31	$243.30	$243.30
Purchase #4	$97.79	4.469%	$102.1602	$102.16	$102.15	$102.20
Purchase #5	$109.26	6.234%	$116.0713	$116.07	$116.05	$116.10
Purchase #6	$39.32	8.424%	$42.6323	$42.63	$42.65	$42.60
Purchase #7	$100.43	9.162%	$109.6314	$109.63	$109.65	$109.60
7 purchase totals =	$830.77		$883.0616	$883.05	$883.05	$883.00