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	$246.76	12.111%	$276.6451	$276.65	$276.65	$276.60
Purchase #2	$25.86	11.513%	$28.8373	$28.84	$28.85	$28.80
Purchase #3	$195.89	10.505%	$216.4682	$216.47	$216.45	$216.50
Purchase #4	$101.29	4.511%	$105.8592	$105.86	$105.85	$105.90
Purchase #5	$242.75	10.475%	$268.1781	$268.18	$268.20	$268.20
Purchase #6	$232.83	13.794%	$264.9466	$264.95	$264.95	$264.90
Purchase #7	$78.70	5.387%	$82.9396	$82.94	$82.95	$82.90
7 purchase totals =	$1,124.08		$1,243.8741	$1,243.89	$1,243.90	$1,243.80