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	$182.51	4.780%	$191.234	$191.23	$191.25	$191.20
Purchase #2	$93.91	11.237%	$104.4627	$104.46	$104.45	$104.50
Purchase #3	$93.44	5.761%	$98.8231	$98.82	$98.80	$98.80
Purchase #4	$168.82	11.153%	$187.6485	$187.65	$187.65	$187.60
Purchase #5	$31.65	3.358%	$32.7128	$32.71	$32.70	$32.70
Purchase #6	$148.76	7.665%	$160.1625	$160.16	$160.15	$160.20
Purchase #7	$68.57	7.716%	$73.8609	$73.86	$73.85	$73.90
7 purchase totals =	$787.66		$848.9045	$848.89	$848.85	$848.90