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	$134.74	11.710%	$150.5181	$150.52	$150.50	$150.50
Purchase #2	$59.76	9.645%	$65.5239	$65.52	$65.50	$65.50
Purchase #3	$13.91	11.697%	$15.5371	$15.54	$15.55	$15.50
Purchase #4	$222.69	4.292%	$232.2479	$232.25	$232.25	$232.20
Purchase #5	$147.66	5.731%	$156.1224	$156.12	$156.10	$156.10
Purchase #6	$140.80	13.826%	$160.267	$160.27	$160.25	$160.30
Purchase #7	$117.74	4.453%	$122.983	$122.98	$123.00	$123.00
7 purchase totals =	$837.30		$903.1994	$903.20	$903.15	$903.10