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	$47.69	12.151%	$53.4848	$53.48	$53.50	$53.50
Purchase #2	$222.87	12.245%	$250.1604	$250.16	$250.15	$250.20
Purchase #3	$86.79	11.478%	$96.7518	$96.75	$96.75	$96.80
Purchase #4	$133.98	9.836%	$147.1583	$147.16	$147.15	$147.20
Purchase #5	$169.97	5.648%	$179.5699	$179.57	$179.55	$179.60
Purchase #6	$239.67	13.257%	$271.4431	$271.44	$271.45	$271.40
Purchase #7	$82.76	9.314%	$90.4683	$90.47	$90.45	$90.50
7 purchase totals =	$983.73		$1,089.0366	$1,089.03	$1,089.00	$1,089.20