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	$49.33	9.550%	$54.041	$54.04	$54.05	$54.00
Purchase #2	$131.86	8.455%	$143.0088	$143.01	$143.00	$143.00
Purchase #3	$173.64	10.264%	$191.4624	$191.46	$191.45	$191.50
Purchase #4	$120.32	7.686%	$129.5678	$129.57	$129.55	$129.60
Purchase #5	$220.92	9.321%	$241.512	$241.51	$241.50	$241.50
Purchase #6	$239.54	6.719%	$255.6347	$255.63	$255.65	$255.60
Purchase #7	$230.98	8.375%	$250.3246	$250.32	$250.30	$250.30
7 purchase totals =	$1,166.59		$1,265.5513	$1,265.54	$1,265.50	$1,265.50