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	$171.77	6.124%	$182.2892	$182.29	$182.30	$182.30
Purchase #2	$180.45	11.298%	$200.8372	$200.84	$200.85	$200.80
Purchase #3	$174.50	3.848%	$181.2148	$181.21	$181.20	$181.20
Purchase #4	$100.45	6.578%	$107.0576	$107.06	$107.05	$107.10
Purchase #5	$221.27	9.837%	$243.0363	$243.04	$243.05	$243.00
Purchase #6	$152.98	4.855%	$160.4072	$160.41	$160.40	$160.40
Purchase #7	$98.33	13.328%	$111.4354	$111.44	$111.45	$111.40
7 purchase totals =	$1,099.75		$1,186.2777	$1,186.29	$1,186.30	$1,186.20