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	$88.69	12.766%	$100.0122	$100.01	$100.00	$100.00
Purchase #2	$102.91	6.683%	$109.7875	$109.79	$109.80	$109.80
Purchase #3	$80.96	10.409%	$89.3871	$89.39	$89.40	$89.40
Purchase #4	$145.42	5.228%	$153.0226	$153.02	$153.00	$153.00
Purchase #5	$140.57	6.695%	$149.9812	$149.98	$150.00	$150.00
Purchase #6	$240.45	10.319%	$265.262	$265.26	$265.25	$265.30
Purchase #7	$196.61	6.840%	$210.0581	$210.06	$210.05	$210.10
7 purchase totals =	$995.61		$1,077.5107	$1,077.51	$1,077.50	$1,077.60