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	$72.56	6.514%	$77.2866	$77.29	$77.30	$77.30
Purchase #2	$250.53	13.705%	$284.8651	$284.87	$284.85	$284.90
Purchase #3	$234.80	7.205%	$251.7173	$251.72	$251.70	$251.70
Purchase #4	$67.57	7.246%	$72.4661	$72.47	$72.45	$72.50
Purchase #5	$78.99	13.400%	$89.5747	$89.57	$89.55	$89.60
Purchase #6	$242.34	11.588%	$270.4224	$270.42	$270.40	$270.40
Purchase #7	$202.28	9.494%	$221.4845	$221.48	$221.50	$221.50
7 purchase totals =	$1,149.07		$1,267.8167	$1,267.82	$1,267.75	$1,267.90