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	$170.86	11.499%	$190.5072	$190.51	$190.50	$190.50
Purchase #2	$117.89	8.836%	$128.3068	$128.31	$128.30	$128.30
Purchase #3	$93.69	6.345%	$99.6346	$99.63	$99.65	$99.60
Purchase #4	$170.42	8.214%	$184.4183	$184.42	$184.40	$184.40
Purchase #5	$35.37	5.873%	$37.4473	$37.45	$37.45	$37.40
Purchase #6	$115.79	10.445%	$127.8843	$127.88	$127.90	$127.90
Purchase #7	$58.99	7.183%	$63.2273	$63.23	$63.25	$63.20
7 purchase totals =	$763.01		$831.4258	$831.43	$831.45	$831.30