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	$62.99	12.822%	$71.0666	$71.07	$71.05	$71.10
Purchase #2	$125.27	13.768%	$142.5172	$142.52	$142.50	$142.50
Purchase #3	$76.32	6.324%	$81.1465	$81.15	$81.15	$81.10
Purchase #4	$223.56	13.756%	$254.3129	$254.31	$254.30	$254.30
Purchase #5	$41.41	4.548%	$43.2933	$43.29	$43.30	$43.30
Purchase #6	$191.71	4.510%	$200.3561	$200.36	$200.35	$200.40
Purchase #7	$197.38	3.213%	$203.7218	$203.72	$203.70	$203.70
7 purchase totals =	$918.64		$996.4144	$996.42	$996.35	$996.40