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	$57.82	5.681%	$61.1048	$61.10	$61.10	$61.10
Purchase #2	$172.51	8.558%	$187.2734	$187.27	$187.25	$187.30
Purchase #3	$240.87	11.224%	$267.9052	$267.91	$267.90	$267.90
Purchase #4	$20.71	5.837%	$21.9188	$21.92	$21.90	$21.90
Purchase #5	$19.88	12.801%	$22.4248	$22.42	$22.40	$22.40
Purchase #6	$99.70	9.591%	$109.2622	$109.26	$109.25	$109.30
Purchase #7	$57.92	9.263%	$63.2851	$63.29	$63.30	$63.30
7 purchase totals =	$669.41		$733.1743	$733.17	$733.10	$733.20