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	$195.91	13.583%	$222.5205	$222.52	$222.50	$222.50
Purchase #2	$237.51	4.789%	$248.8844	$248.88	$248.90	$248.90
Purchase #3	$214.76	3.629%	$222.5536	$222.55	$222.55	$222.60
Purchase #4	$38.75	13.191%	$43.8615	$43.86	$43.85	$43.90
Purchase #5	$7.54	3.801%	$7.8266	$7.83	$7.85	$7.80
Purchase #6	$155.60	13.180%	$176.1081	$176.11	$176.10	$176.10
Purchase #7	$190.76	11.872%	$213.407	$213.41	$213.40	$213.40
7 purchase totals =	$1,040.83		$1,135.1617	$1,135.16	$1,135.15	$1,135.20