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	$75.85	3.502%	$78.5063	$78.51	$78.50	$78.50
Purchase #2	$60.47	3.157%	$62.379	$62.38	$62.40	$62.40
Purchase #3	$28.62	12.201%	$32.1119	$32.11	$32.10	$32.10
Purchase #4	$136.91	3.781%	$142.0866	$142.09	$142.10	$142.10
Purchase #5	$171.75	9.519%	$188.0989	$188.10	$188.10	$188.10
Purchase #6	$216.46	3.188%	$223.3607	$223.36	$223.35	$223.40
Purchase #7	$28.56	9.631%	$31.3106	$31.31	$31.30	$31.30
7 purchase totals =	$718.62		$757.8540	$757.86	$757.85	$757.90