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	$157.91	10.364%	$174.2758	$174.28	$174.30	$174.30
Purchase #2	$221.94	6.186%	$235.6692	$235.67	$235.65	$235.70
Purchase #3	$21.25	8.625%	$23.0828	$23.08	$23.10	$23.10
Purchase #4	$127.50	3.167%	$131.5379	$131.54	$131.55	$131.50
Purchase #5	$97.48	8.628%	$105.8906	$105.89	$105.90	$105.90
Purchase #6	$92.50	3.262%	$95.5174	$95.52	$95.50	$95.50
Purchase #7	$171.72	10.552%	$189.8399	$189.84	$189.85	$189.80
7 purchase totals =	$890.30		$955.8136	$955.82	$955.85	$955.80