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	$60.99	6.864%	$65.1764	$65.18	$65.20	$65.20
Purchase #2	$48.96	8.865%	$53.3003	$53.30	$53.30	$53.30
Purchase #3	$43.84	10.277%	$48.3454	$48.35	$48.35	$48.30
Purchase #4	$118.47	7.477%	$127.328	$127.33	$127.35	$127.30
Purchase #5	$229.53	9.764%	$251.9413	$251.94	$251.95	$251.90
Purchase #6	$31.32	8.120%	$33.8632	$33.86	$33.85	$33.90
Purchase #7	$36.35	12.552%	$40.9127	$40.91	$40.90	$40.90
7 purchase totals =	$569.46		$620.8673	$620.87	$620.90	$620.80