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	$87.29	3.836%	$90.6384	$90.64	$90.65	$90.60
Purchase #2	$98.51	11.617%	$109.9539	$109.95	$109.95	$110.00
Purchase #3	$249.51	8.741%	$271.3197	$271.32	$271.30	$271.30
Purchase #4	$180.41	7.703%	$194.307	$194.31	$194.30	$194.30
Purchase #5	$130.41	5.606%	$137.7208	$137.72	$137.70	$137.70
Purchase #6	$239.95	4.347%	$250.3806	$250.38	$250.40	$250.40
Purchase #7	$69.53	7.236%	$74.5612	$74.56	$74.55	$74.60
7 purchase totals =	$1,055.61		$1,128.8816	$1,128.88	$1,128.85	$1,128.90