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	$246.41	11.396%	$274.4909	$274.49	$274.50	$274.50
Purchase #2	$134.66	6.642%	$143.6041	$143.60	$143.60	$143.60
Purchase #3	$41.56	3.741%	$43.1148	$43.11	$43.10	$43.10
Purchase #4	$6.98	13.223%	$7.903	$7.90	$7.90	$7.90
Purchase #5	$128.29	12.284%	$144.0491	$144.05	$144.05	$144.00
Purchase #6	$189.99	3.525%	$196.6871	$196.69	$196.70	$196.70
Purchase #7	$42.70	13.674%	$48.5388	$48.54	$48.55	$48.50
7 purchase totals =	$790.59		$858.3878	$858.38	$858.40	$858.30