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	$39.61	6.212%	$42.0706	$42.07	$42.05	$42.10
Purchase #2	$181.81	4.369%	$189.7533	$189.75	$189.75	$189.80
Purchase #3	$33.42	9.424%	$36.5695	$36.57	$36.55	$36.60
Purchase #4	$175.53	13.777%	$199.7128	$199.71	$199.70	$199.70
Purchase #5	$178.39	11.150%	$198.2805	$198.28	$198.30	$198.30
Purchase #6	$39.38	7.418%	$42.3012	$42.30	$42.30	$42.30
Purchase #7	$95.72	3.114%	$98.7007	$98.70	$98.70	$98.70
7 purchase totals =	$743.86		$807.3886	$807.38	$807.35	$807.50