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	$88.91	12.149%	$99.7117	$99.71	$99.70	$99.70
Purchase #2	$215.27	7.618%	$231.6693	$231.67	$231.65	$231.70
Purchase #3	$88.25	12.507%	$99.2874	$99.29	$99.30	$99.30
Purchase #4	$140.50	3.343%	$145.1969	$145.20	$145.20	$145.20
Purchase #5	$102.31	3.556%	$105.9481	$105.95	$105.95	$105.90
Purchase #6	$137.36	7.636%	$147.8488	$147.85	$147.85	$147.80
Purchase #7	$43.55	7.564%	$46.8441	$46.84	$46.85	$46.80
7 purchase totals =	$816.15		$876.5063	$876.51	$876.50	$876.40