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	$55.40	5.817%	$58.6226	$58.62	$58.60	$58.60
Purchase #2	$105.26	10.596%	$116.4133	$116.41	$116.40	$116.40
Purchase #3	$248.35	10.674%	$274.8589	$274.86	$274.85	$274.90
Purchase #4	$232.96	4.552%	$243.5643	$243.56	$243.55	$243.60
Purchase #5	$216.77	5.698%	$229.1216	$229.12	$229.10	$229.10
Purchase #6	$186.48	12.681%	$210.1275	$210.13	$210.15	$210.10
Purchase #7	$85.44	5.340%	$90.0025	$90.00	$90.00	$90.00
7 purchase totals =	$1,130.66		$1,222.7107	$1,222.70	$1,222.65	$1,222.70