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	$133.77	6.377%	$142.3005	$142.30	$142.30	$142.30
Purchase #2	$181.69	5.577%	$191.8229	$191.82	$191.80	$191.80
Purchase #3	$245.41	8.349%	$265.8993	$265.90	$265.90	$265.90
Purchase #4	$110.33	7.595%	$118.7096	$118.71	$118.70	$118.70
Purchase #5	$236.96	12.468%	$266.5042	$266.50	$266.50	$266.50
Purchase #6	$49.33	10.859%	$54.6867	$54.69	$54.70	$54.70
Purchase #7	$87.88	5.163%	$92.4172	$92.42	$92.40	$92.40
7 purchase totals =	$1,045.37		$1,132.3404	$1,132.34	$1,132.30	$1,132.30