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	$99.98	6.609%	$106.5877	$106.59	$106.60	$106.60
Purchase #2	$97.34	6.457%	$103.6252	$103.63	$103.65	$103.60
Purchase #3	$32.31	6.164%	$34.3016	$34.30	$34.30	$34.30
Purchase #4	$157.42	6.196%	$167.1737	$167.17	$167.15	$167.20
Purchase #5	$182.71	10.197%	$201.3409	$201.34	$201.35	$201.30
Purchase #6	$140.28	7.679%	$151.0521	$151.05	$151.05	$151.10
Purchase #7	$74.71	5.582%	$78.8803	$78.88	$78.90	$78.90
7 purchase totals =	$784.75		$842.9615	$842.96	$843.00	$843.00