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	$231.95	8.232%	$251.0441	$251.04	$251.05	$251.00
Purchase #2	$88.96	11.703%	$99.371	$99.37	$99.35	$99.40
Purchase #3	$177.51	6.667%	$189.3446	$189.34	$189.35	$189.30
Purchase #4	$99.68	9.584%	$109.2333	$109.23	$109.25	$109.20
Purchase #5	$85.46	8.188%	$92.4575	$92.46	$92.45	$92.50
Purchase #6	$129.55	10.107%	$142.6436	$142.64	$142.65	$142.60
Purchase #7	$39.32	6.337%	$41.8117	$41.81	$41.80	$41.80
7 purchase totals =	$852.43		$925.9058	$925.89	$925.90	$925.80