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	$234.60	10.215%	$258.5644	$258.56	$258.55	$258.60
Purchase #2	$239.46	13.128%	$270.8963	$270.90	$270.90	$270.90
Purchase #3	$51.74	4.295%	$53.9622	$53.96	$53.95	$54.00
Purchase #4	$39.58	7.294%	$42.467	$42.47	$42.45	$42.50
Purchase #5	$73.67	11.465%	$82.1163	$82.12	$82.10	$82.10
Purchase #6	$242.57	3.331%	$250.65	$250.65	$250.65	$250.70
Purchase #7	$88.39	11.471%	$98.5292	$98.53	$98.55	$98.50
7 purchase totals =	$970.01		$1,057.1854	$1,057.19	$1,057.15	$1,057.30