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	$71.27	10.783%	$78.955	$78.96	$78.95	$79.00
Purchase #2	$135.99	11.301%	$151.3582	$151.36	$151.35	$151.40
Purchase #3	$244.91	12.279%	$274.9825	$274.98	$275.00	$275.00
Purchase #4	$109.76	12.620%	$123.6117	$123.61	$123.60	$123.60
Purchase #5	$103.30	3.401%	$106.8132	$106.81	$106.80	$106.80
Purchase #6	$215.25	9.199%	$235.0508	$235.05	$235.05	$235.10
Purchase #7	$219.38	4.598%	$229.4671	$229.47	$229.45	$229.50
7 purchase totals =	$1,099.86		$1,200.2385	$1,200.24	$1,200.20	$1,200.40