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	$63.97	12.530%	$71.9854	$71.99	$72.00	$72.00
Purchase #2	$128.89	6.392%	$137.1286	$137.13	$137.15	$137.10
Purchase #3	$127.93	7.250%	$137.2049	$137.20	$137.20	$137.20
Purchase #4	$97.52	7.580%	$104.912	$104.91	$104.90	$104.90
Purchase #5	$224.82	8.223%	$243.3069	$243.31	$243.30	$243.30
Purchase #6	$37.69	6.374%	$40.0924	$40.09	$40.10	$40.10
Purchase #7	$184.27	5.416%	$194.2501	$194.25	$194.25	$194.30
7 purchase totals =	$865.09		$928.8803	$928.88	$928.90	$928.90