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	$52.38	9.456%	$57.3331	$57.33	$57.35	$57.30
Purchase #2	$68.33	5.194%	$71.8791	$71.88	$71.90	$71.90
Purchase #3	$9.57	10.243%	$10.5503	$10.55	$10.55	$10.60
Purchase #4	$225.49	3.465%	$233.3032	$233.30	$233.30	$233.30
Purchase #5	$61.89	13.651%	$70.3386	$70.34	$70.35	$70.30
Purchase #6	$229.56	3.724%	$238.1088	$238.11	$238.10	$238.10
Purchase #7	$53.67	7.682%	$57.7929	$57.79	$57.80	$57.80
7 purchase totals =	$700.89		$739.3060	$739.30	$739.35	$739.30