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	$53.33	8.789%	$58.0172	$58.02	$58.00	$58.00
Purchase #2	$129.34	9.394%	$141.4902	$141.49	$141.50	$141.50
Purchase #3	$37.82	11.781%	$42.2756	$42.28	$42.30	$42.30
Purchase #4	$128.70	12.219%	$144.4259	$144.43	$144.45	$144.40
Purchase #5	$7.43	4.259%	$7.7464	$7.75	$7.75	$7.70
Purchase #6	$64.53	10.677%	$71.4199	$71.42	$71.40	$71.40
Purchase #7	$114.53	9.618%	$125.5455	$125.55	$125.55	$125.50
7 purchase totals =	$535.68		$590.9207	$590.94	$590.95	$590.80