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	$239.44	7.377%	$257.1035	$257.10	$257.10	$257.10
Purchase #2	$42.81	10.508%	$47.3085	$47.31	$47.30	$47.30
Purchase #3	$152.29	6.608%	$162.3533	$162.35	$162.35	$162.40
Purchase #4	$78.95	9.336%	$86.3208	$86.32	$86.30	$86.30
Purchase #5	$91.28	9.568%	$100.0137	$100.01	$100.00	$100.00
Purchase #6	$60.65	10.855%	$67.2336	$67.23	$67.25	$67.20
Purchase #7	$118.71	10.600%	$131.2933	$131.29	$131.30	$131.30
7 purchase totals =	$784.13		$851.6267	$851.61	$851.60	$851.60