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	$72.63	11.214%	$80.7747	$80.77	$80.75	$80.80
Purchase #2	$64.54	3.859%	$67.0306	$67.03	$67.05	$67.00
Purchase #3	$196.50	7.609%	$211.4517	$211.45	$211.45	$211.50
Purchase #4	$203.91	3.139%	$210.3107	$210.31	$210.30	$210.30
Purchase #5	$216.42	7.752%	$233.1969	$233.20	$233.20	$233.20
Purchase #6	$210.65	7.829%	$227.1418	$227.14	$227.15	$227.10
Purchase #7	$85.95	5.343%	$90.5423	$90.54	$90.55	$90.50
7 purchase totals =	$1,050.60		$1,120.4487	$1,120.44	$1,120.45	$1,120.40