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	$155.80	10.214%	$171.7134	$171.71	$171.70	$171.70
Purchase #2	$141.48	12.497%	$159.1608	$159.16	$159.15	$159.20
Purchase #3	$224.42	13.368%	$254.4205	$254.42	$254.40	$254.40
Purchase #4	$197.31	11.259%	$219.5251	$219.53	$219.55	$219.50
Purchase #5	$70.32	11.442%	$78.366	$78.37	$78.35	$78.40
Purchase #6	$199.67	6.621%	$212.8902	$212.89	$212.90	$212.90
Purchase #7	$228.46	4.304%	$238.2929	$238.29	$238.30	$238.30
7 purchase totals =	$1,217.46		$1,334.3689	$1,334.37	$1,334.35	$1,334.40