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	$238.88	5.192%	$251.2826	$251.28	$251.30	$251.30
Purchase #2	$37.76	12.223%	$42.3754	$42.38	$42.40	$42.40
Purchase #3	$55.31	10.855%	$61.3139	$61.31	$61.30	$61.30
Purchase #4	$190.42	3.124%	$196.3687	$196.37	$196.35	$196.40
Purchase #5	$68.64	8.404%	$74.4085	$74.41	$74.40	$74.40
Purchase #6	$38.49	13.546%	$43.7039	$43.70	$43.70	$43.70
Purchase #7	$111.34	8.572%	$120.8841	$120.88	$120.90	$120.90
7 purchase totals =	$740.84		$790.3371	$790.33	$790.35	$790.40