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	$119.84	6.573%	$127.7171	$127.72	$127.70	$127.70
Purchase #2	$151.33	8.484%	$164.1688	$164.17	$164.15	$164.20
Purchase #3	$246.47	11.118%	$273.8725	$273.87	$273.85	$273.90
Purchase #4	$86.83	13.661%	$98.6918	$98.69	$98.70	$98.70
Purchase #5	$250.35	3.791%	$259.8408	$259.84	$259.85	$259.80
Purchase #6	$153.53	4.310%	$160.1471	$160.15	$160.15	$160.10
Purchase #7	$97.64	8.280%	$105.7246	$105.72	$105.70	$105.70
7 purchase totals =	$1,105.99		$1,190.1627	$1,190.16	$1,190.10	$1,190.10