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	$180.72	13.168%	$204.5172	$204.52	$204.50	$204.50
Purchase #2	$149.58	12.230%	$167.8736	$167.87	$167.85	$167.90
Purchase #3	$81.41	6.150%	$86.4167	$86.42	$86.40	$86.40
Purchase #4	$188.51	6.263%	$200.3164	$200.32	$200.30	$200.30
Purchase #5	$77.45	10.728%	$85.7588	$85.76	$85.75	$85.80
Purchase #6	$65.31	10.418%	$72.114	$72.11	$72.10	$72.10
Purchase #7	$208.48	6.465%	$221.9582	$221.96	$221.95	$222.00
7 purchase totals =	$951.46		$1,038.9549	$1,038.96	$1,038.85	$1,039.00