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	$76.33	4.164%	$79.5084	$79.51	$79.50	$79.50
Purchase #2	$245.71	3.562%	$254.4622	$254.46	$254.45	$254.50
Purchase #3	$233.34	7.261%	$250.2828	$250.28	$250.30	$250.30
Purchase #4	$149.56	7.698%	$161.0731	$161.07	$161.05	$161.10
Purchase #5	$18.38	6.293%	$19.5367	$19.54	$19.55	$19.50
Purchase #6	$23.45	6.265%	$24.9191	$24.92	$24.90	$24.90
Purchase #7	$80.51	11.277%	$89.5891	$89.59	$89.60	$89.60
7 purchase totals =	$827.28		$879.3714	$879.37	$879.35	$879.40