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	$245.37	12.159%	$275.2045	$275.20	$275.20	$275.20
Purchase #2	$136.39	11.305%	$151.8089	$151.81	$151.80	$151.80
Purchase #3	$76.54	12.264%	$85.9269	$85.93	$85.95	$85.90
Purchase #4	$210.71	4.317%	$219.8064	$219.81	$219.80	$219.80
Purchase #5	$247.32	11.835%	$276.5903	$276.59	$276.60	$276.60
Purchase #6	$151.81	13.553%	$172.3848	$172.38	$172.40	$172.40
Purchase #7	$99.43	10.370%	$109.7409	$109.74	$109.75	$109.70
7 purchase totals =	$1,167.57		$1,291.4627	$1,291.46	$1,291.50	$1,291.40