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	$43.28	3.793%	$44.9216	$44.92	$44.90	$44.90
Purchase #2	$132.45	7.549%	$142.4487	$142.45	$142.45	$142.40
Purchase #3	$80.33	10.408%	$88.6907	$88.69	$88.70	$88.70
Purchase #4	$89.89	9.173%	$98.1356	$98.14	$98.15	$98.10
Purchase #5	$7.51	3.185%	$7.7492	$7.75	$7.75	$7.70
Purchase #6	$207.66	7.822%	$223.9032	$223.90	$223.90	$223.90
Purchase #7	$36.56	13.329%	$41.4331	$41.43	$41.45	$41.40
7 purchase totals =	$597.68		$647.2821	$647.28	$647.30	$647.10