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	$231.56	6.154%	$245.8102	$245.81	$245.80	$245.80
Purchase #2	$62.44	3.289%	$64.4937	$64.49	$64.50	$64.50
Purchase #3	$114.35	4.847%	$119.8925	$119.89	$119.90	$119.90
Purchase #4	$68.94	13.506%	$78.251	$78.25	$78.25	$78.30
Purchase #5	$98.92	5.651%	$104.51	$104.51	$104.50	$104.50
Purchase #6	$52.50	13.194%	$59.4269	$59.43	$59.45	$59.40
Purchase #7	$69.36	11.605%	$77.4092	$77.41	$77.40	$77.40
7 purchase totals =	$698.07		$749.7935	$749.79	$749.80	$749.80