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	$51.43	11.601%	$57.3964	$57.40	$57.40	$57.40
Purchase #2	$145.80	5.552%	$153.8948	$153.89	$153.90	$153.90
Purchase #3	$218.92	10.432%	$241.7577	$241.76	$241.75	$241.80
Purchase #4	$212.38	13.262%	$240.5458	$240.55	$240.55	$240.50
Purchase #5	$246.50	11.516%	$274.8869	$274.89	$274.90	$274.90
Purchase #6	$135.46	13.330%	$153.5168	$153.52	$153.50	$153.50
Purchase #7	$85.36	6.511%	$90.9178	$90.92	$90.90	$90.90
7 purchase totals =	$1,095.85		$1,212.9162	$1,212.93	$1,212.90	$1,212.90