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	$140.51	7.711%	$151.3447	$151.34	$151.35	$151.30
Purchase #2	$127.49	9.750%	$139.9203	$139.92	$139.90	$139.90
Purchase #3	$238.90	12.721%	$269.2905	$269.29	$269.30	$269.30
Purchase #4	$100.79	13.835%	$114.7343	$114.73	$114.75	$114.70
Purchase #5	$29.43	13.155%	$33.3015	$33.30	$33.30	$33.30
Purchase #6	$42.96	13.862%	$48.9151	$48.92	$48.90	$48.90
Purchase #7	$119.63	3.415%	$123.7154	$123.72	$123.70	$123.70
7 purchase totals =	$799.71		$881.2218	$881.22	$881.20	$881.10