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	$24.71	10.107%	$27.2074	$27.21	$27.20	$27.20
Purchase #2	$133.72	7.171%	$143.3091	$143.31	$143.30	$143.30
Purchase #3	$50.37	6.386%	$53.5866	$53.59	$53.60	$53.60
Purchase #4	$111.61	10.545%	$123.3793	$123.38	$123.40	$123.40
Purchase #5	$198.82	10.765%	$220.223	$220.22	$220.20	$220.20
Purchase #6	$204.41	11.651%	$228.2258	$228.23	$228.25	$228.20
Purchase #7	$171.60	8.176%	$185.63	$185.63	$185.65	$185.60
7 purchase totals =	$895.24		$981.5612	$981.57	$981.60	$981.50