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	$189.67	10.621%	$209.8149	$209.81	$209.80	$209.80
Purchase #2	$38.46	4.199%	$40.0749	$40.07	$40.05	$40.10
Purchase #3	$36.83	3.707%	$38.1953	$38.20	$38.20	$38.20
Purchase #4	$179.82	4.602%	$188.0953	$188.10	$188.10	$188.10
Purchase #5	$100.65	9.801%	$110.5147	$110.51	$110.50	$110.50
Purchase #6	$25.37	11.507%	$28.2893	$28.29	$28.30	$28.30
Purchase #7	$35.81	8.608%	$38.8925	$38.89	$38.90	$38.90
7 purchase totals =	$606.61		$653.8769	$653.87	$653.85	$653.90