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	$141.32	9.834%	$155.2174	$155.22	$155.20	$155.20
Purchase #2	$141.72	6.493%	$150.9219	$150.92	$150.90	$150.90
Purchase #3	$128.43	10.505%	$141.9216	$141.92	$141.90	$141.90
Purchase #4	$76.74	4.846%	$80.4588	$80.46	$80.45	$80.50
Purchase #5	$119.36	11.807%	$133.4528	$133.45	$133.45	$133.50
Purchase #6	$65.29	12.222%	$73.2697	$73.27	$73.25	$73.30
Purchase #7	$52.65	9.570%	$57.6886	$57.69	$57.70	$57.70
7 purchase totals =	$725.51		$792.9308	$792.93	$792.85	$793.00