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	$224.53	3.465%	$232.31	$232.31	$232.30	$232.30
Purchase #2	$91.39	10.582%	$101.0609	$101.06	$101.05	$101.10
Purchase #3	$120.43	6.645%	$128.4326	$128.43	$128.45	$128.40
Purchase #4	$181.72	6.506%	$193.5427	$193.54	$193.55	$193.50
Purchase #5	$82.25	11.747%	$91.9119	$91.91	$91.90	$91.90
Purchase #6	$38.99	10.816%	$43.2072	$43.21	$43.20	$43.20
Purchase #7	$176.77	6.583%	$188.4068	$188.41	$188.40	$188.40
7 purchase totals =	$916.08		$978.8721	$978.87	$978.85	$978.80