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	$170.77	6.290%	$181.5114	$181.51	$181.50	$181.50
Purchase #2	$139.60	5.369%	$147.0951	$147.10	$147.10	$147.10
Purchase #3	$67.37	13.573%	$76.5141	$76.51	$76.50	$76.50
Purchase #4	$194.46	9.196%	$212.3425	$212.34	$212.35	$212.30
Purchase #5	$51.90	11.461%	$57.8483	$57.85	$57.85	$57.80
Purchase #6	$211.31	12.689%	$238.1231	$238.12	$238.10	$238.10
Purchase #7	$215.98	4.468%	$225.63	$225.63	$225.65	$225.60
7 purchase totals =	$1,051.39		$1,139.0645	$1,139.06	$1,139.05	$1,138.90