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	$121.30	12.856%	$136.8943	$136.89	$136.90	$136.90
Purchase #2	$134.39	13.740%	$152.8552	$152.86	$152.85	$152.90
Purchase #3	$84.63	4.736%	$88.6381	$88.64	$88.65	$88.60
Purchase #4	$41.33	13.145%	$46.7628	$46.76	$46.75	$46.80
Purchase #5	$39.58	7.121%	$42.3985	$42.40	$42.40	$42.40
Purchase #6	$123.31	3.158%	$127.2041	$127.20	$127.20	$127.20
Purchase #7	$76.99	7.567%	$82.8158	$82.82	$82.80	$82.80
7 purchase totals =	$621.53		$677.5688	$677.57	$677.55	$677.60