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	$136.96	5.298%	$144.2161	$144.22	$144.20	$144.20
Purchase #2	$65.55	10.655%	$72.5344	$72.53	$72.55	$72.50
Purchase #3	$36.95	3.458%	$38.2277	$38.23	$38.25	$38.20
Purchase #4	$209.81	7.288%	$225.101	$225.10	$225.10	$225.10
Purchase #5	$79.64	4.562%	$83.2732	$83.27	$83.25	$83.30
Purchase #6	$39.61	5.290%	$41.7054	$41.71	$41.70	$41.70
Purchase #7	$10.93	12.297%	$12.2741	$12.27	$12.25	$12.30
7 purchase totals =	$579.45		$617.3319	$617.33	$617.30	$617.30