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	$82.26	9.814%	$90.333	$90.33	$90.35	$90.30
Purchase #2	$58.91	8.415%	$63.8673	$63.87	$63.85	$63.90
Purchase #3	$27.57	3.830%	$28.6259	$28.63	$28.65	$28.60
Purchase #4	$57.43	7.191%	$61.5598	$61.56	$61.55	$61.60
Purchase #5	$140.65	10.237%	$155.0483	$155.05	$155.05	$155.00
Purchase #6	$216.37	12.567%	$243.5612	$243.56	$243.55	$243.60
Purchase #7	$150.31	11.734%	$167.9474	$167.95	$167.95	$167.90
7 purchase totals =	$733.50		$810.9429	$810.95	$810.95	$810.90