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	$165.47	13.577%	$187.9359	$187.94	$187.95	$187.90
Purchase #2	$225.91	10.722%	$250.1321	$250.13	$250.15	$250.10
Purchase #3	$81.52	11.483%	$90.8809	$90.88	$90.90	$90.90
Purchase #4	$85.52	4.522%	$89.3872	$89.39	$89.40	$89.40
Purchase #5	$169.72	7.201%	$181.9415	$181.94	$181.95	$181.90
Purchase #6	$119.61	3.168%	$123.3992	$123.40	$123.40	$123.40
Purchase #7	$152.47	10.369%	$168.2796	$168.28	$168.30	$168.30
7 purchase totals =	$1,000.22		$1,091.9564	$1,091.96	$1,092.05	$1,091.90