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	$28.51	12.231%	$31.9971	$32.00	$32.00	$32.00
Purchase #2	$52.54	12.740%	$59.2336	$59.23	$59.25	$59.20
Purchase #3	$117.99	4.857%	$123.7208	$123.72	$123.70	$123.70
Purchase #4	$213.51	12.476%	$240.1475	$240.15	$240.15	$240.10
Purchase #5	$191.80	11.394%	$213.6537	$213.65	$213.65	$213.70
Purchase #6	$142.49	5.803%	$150.7587	$150.76	$150.75	$150.80
Purchase #7	$45.36	11.851%	$50.7356	$50.74	$50.75	$50.70
7 purchase totals =	$792.20		$870.2470	$870.25	$870.25	$870.20