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	$250.41	8.111%	$270.7208	$270.72	$270.70	$270.70
Purchase #2	$74.98	11.634%	$83.7032	$83.70	$83.70	$83.70
Purchase #3	$162.25	4.663%	$169.8157	$169.82	$169.80	$169.80
Purchase #4	$35.83	3.314%	$37.0174	$37.02	$37.00	$37.00
Purchase #5	$164.77	5.763%	$174.2657	$174.27	$174.25	$174.30
Purchase #6	$142.65	9.622%	$156.3758	$156.38	$156.40	$156.40
Purchase #7	$174.97	13.296%	$198.234	$198.23	$198.25	$198.20
7 purchase totals =	$1,005.86		$1,090.1326	$1,090.14	$1,090.10	$1,090.10