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	$68.65	3.841%	$71.2868	$71.29	$71.30	$71.30
Purchase #2	$32.34	7.474%	$34.7571	$34.76	$34.75	$34.80
Purchase #3	$95.72	4.327%	$99.8618	$99.86	$99.85	$99.90
Purchase #4	$144.70	7.657%	$155.7797	$155.78	$155.80	$155.80
Purchase #5	$157.37	10.760%	$174.303	$174.30	$174.30	$174.30
Purchase #6	$57.34	3.226%	$59.1898	$59.19	$59.20	$59.20
Purchase #7	$19.61	7.146%	$21.0113	$21.01	$21.00	$21.00
7 purchase totals =	$575.73		$616.1895	$616.19	$616.20	$616.30